So I had some free time tonight and got sidetracked. This is the result of that.
Acrobatics
Physical Boost (Conditional; +1d4; Applies to one roll only)
Quicksilver Mutagen (Item; +2-5; 1 min to 1 hour)
Slick Rune (Item; +2 or +4; Applies to either Escape or Squeeze checks)
Anklets of Alacrity (Item; +4)
Boots of Elvenkind (Item; +2 or +4)
Cloak of the Bat (Item; +2 to +4; Applies to Maneuver in Flight)
Daredevil Boots (Item +3 or +5; Conditional +1 or +2 to Tumble Through only)
Electric Eelskin (Item; +3)
Salve of Slipperiness (Item; +4; Applies to Escape or Squeeze only)
Arcana
Alchemical Savant (Circumstance; +2; Applies to Identify Magic checks on Alchemical items only; Alchemist)
Cognitive Mutagen (Item; +2-5; 1 min to 1 hour)
Hat of the Magi (Item; +2 or +4)
Ring of Wizardry (Item; +2)
Robe of the Archmagi (Item; +3 or +5)
Athletics
Crane Stance (Conditional; +4; Applies to Jump checks only; Monk)
Climbing Kit (Item; Expert +1; Climb only)
Crowbar (Item; +1; Break Open things that can be pried open only)
Knock (Conditional: +4; Break Open a door, lock, or container)
Physical Boost (Conditional; +1d4; Applies to one roll only)
Beastial Mutagen (Item; +2-5; 1 min to 1 hour based on item level)
Armbands of Athleticism (Item; +3 or +5)
Belt of Giant Strength (Item +4; Conditional +2 to lift heavy objects, Break a Grapple, or Break an Object)
Boots of Bounding (Item; +2 or +4; Applies to Jump only)
Bronze Bull Pendant (Conditional; +2; Applies to Shove only; Single-use)
Horseshoes of Speed (Item; +2 or +4; Applies to High Jump and Long Jump checks only)
Mattock of the Titans (Item; +5; Increases the Belt of Giant Strength item bonus)
Plate Armor of the Deep (Item; +3; Applies to Swim only)
Crafting
Specialty Crafting (Circumstance; +2; Applies on one type of Craft check only; Skill Feat)
Alchemist’s Tools (Item; Expert +1, Master +2; Alchemy only)
Artisan’s Tools (Item; Expert +1, Master +2; Any single Craft type)
Repair Kit (Item; Expert +1; Repair only)
Snare Kit (Item; Expert +1, Master +2; Snares only)
Cognitive Mutagen (Item; +2-5; 1 min to 1 hour)
Alchemist’s Goggles (Item; +2 or +4; Alchemy only)
Crafter’s Eyepiece (Item; +2 or +4; Applies on checks to Craft only)
Inexplicable Apparatus (Item; +5; Applies to checks to Craft or Repair only)
Ring of Maniacal Devices (Item; +3 or +5; Applies to Craft and Repair traps and snares only)
Deception
Lie to Me (Circumstance; +2; Applies once vs enemies that fail to lie or conceal something from you; Skill Feat)
Disguise Kit (Item; Expert +1, Master +2; Disguise only)
Face in the Crowd (Conditional; +2; To go unnoticed in a crowd of similar creatures only)
Silvertongue Mutagen (Item; +2-5; 1 min to 1 hour)
Cape of the Montebank (Item; +3)
Circlet of Persuasion (Item; +3)
Clandestine Cloak (Item; +2 or +4; Applies to Impersonate a forgettable person)
Ring of Lies (Item; +2 or +4)
Whisper of the First Lie (Item; +5)
Diplomacy
Animal Whisperer (Circumstance; +1; Applies to Make an Impression vs Animals; Gnome)
Fey Fellowship (Circumstance; +1; Applies vs Fey only; Gnome)
Green Empathy (Circumstance; +2; Applies to Request vs plants; Druid of the Leaf)
Cultural Familiarity (Circumstance; +1; Applies vs members of one ancestry or ethnicity; Skill Feat)
Lie to Me (Circumstance; +2; Applies once vs enemies that fail to lie or conceal something from you; Skill Feat)
Silvertongue Mutagen (Item; +2-5; 1 min to 1 hour)
Belt of the Five Kings (Conditional; +1; Applies to Make an Impression or Request vs Dwarves)
Breastplate of Command (Item; +2)
Celestial Armor (Item; +3; Applies vs non-fiends)
Circlet of Persuasion (Item; +3)
Clandestine Cloak (Item; +2)
Messenger’s Ring (Item; +3 or +5)
Intimidation
You’re Next (Circumstance; +2; Reaction to Demoralize an enemy only; Rogue)
Intimidating Prowess (Circumstance; +1 or +2; Applies when you can physically menace the target of Coerce or Demoralize; Skill Feat)
Lie to Me (Circumstance; +2; Applies once vs enemies that fail to lie or conceal something from you; Skill Feat)
Silvertongue Mutagen (Item; +2-5; 1 min to 1 hour)
Belt of the Five Kings (Conditional; +1; Applies vs Giants and Orcs)
Demon Mask (Item; +2 or +4)
Gorget of the Primal Roar (Item; +3)
Lore
Cognitive Mutagen (Item; +2-5; 1 min to 1 hour)
Medicine
Healer’s Kit (Item; Expert +1; Administer First Aid, Treat a Disease, and Treat a Poison only)
Bullheaded Mutagen (Item; +2-5; 1 min to 1 hour based on item level.)
Doctor’s Marvelous Medicine (Item; +3 or +5)
Healer’s Gloves (Item; +2 or +4)
Nature
Rough Rider (Circumstance; +1; Applies to Handle vs goblin dog or wolf mounts; Goblin)
Awakened Intellect (Circumstance; +2; Applies to Recall Knowledge checks only; Alchemist)
Bullheaded Mutagen (Item; +2-5; 1 min to 1 hour based on item level.)
Primeval Mistletoe (Item; +2 or +4)
Occultism
Oddity Identification (Circumstance; +2; Applies to Identify Magic with the mental, possession, prediction, or scrying traits; Skill Feat)
Cognitive Mutagen (Item; +2-5; 1 min to 1 hour)
Phylactery of the Occult (Item; +2 or +4)
Perception
Stonecunning (Circumstance; +2; Applies to notice unusual stonework only; Dwarf)
Keen Hearing (Circumstance; +2; Applies to Seek vs creatures within 30’ you can hear; Elf)
Discerning Smell (Circumstance; +2; Applies to Seek vs nearby creatures you can smell; Gnome)
Fey Fellowship (Circumstance; +1; Applies vs Fey only; Gnome)
Illusion Sense (Circumstance; +1; Applies vs Illusions only; Gnome)
Attentive (Circumstance; +2; Applies on Seek checks to notice enchanged or possessed characters only; Halfling)
Keen Eyes (Circumstance; +2; Applies to Seek checks to sense unseen creatures within 30’ only; Halfling)
Hazard Finder (Circumstance; +1; Applies on checks to find traps and hazards only; Ranger)
Trap Finder (Circumstance; +1; Applies on checks to find traps only; Rogue)
Magnifying Glass (Item; +1; To notice minute details only)
Spyglass (Item; +1; Notice details at a distance only)
Discern Lies (Conditional; +4; To detect lies only)
Bullheaded Mutagen (Item; +2-5; 1 min to 1 hour based on item level.)
Eagle-Eye Elixir (Item; +1; Increases to +2 to find secret doors and traps)
Eyes of the Eagle (Item; +2; Applies to checks involving sight only)
Goggles of Night (Item; +2 or +3)
Robe of Eyes (Item; +4)
Third Eye (Item; +5)
Performance
Cultural Familiarity (Circumstance; +1; Applies vs members of one ancestry or ethnicity; Skill Feat)
Lie to Me (Circumstance; +2; Applies once vs enemies that fail to lie or conceal something from you; Skill Feat)
Virtuoso Performer (Circumstance; +2; Applies to one type of Perform check only; Skill Feat)
Musical Instrument (Item; Expert +1, Master +2; Any single Performance type)
Silvertongue Mutagen (Item; +2-5; 1 min to 1 hour)
Dancing Scarf (Item; +2 or +4; Applies to Dance checks only)
Maestro’s Instrument (Item; +3; Applies while playing the instrument only)
Persona Mask (Item; +2 or +4; Applies while acting, orating, performing comedy, or singing)
Virtuoso’s Instrument (Item; +5; Applies while playing the instrument only)
Religion
Awakened Intellect (Circumstance; +2; Applies to Recall Knowledge checks only; Alchemist)
Bullheaded Mutagen (Item; +2-5; 1 min to 1 hour based on item level.)
Phylactery of Faithfulness (Item; +2 or +4)
Thurible of Revelation (Item; +2 or +4)
Society
Cultural Familiarity (Circumstance; +1; Applies to Recall Knowledge about members of one ancestry or ethnicity; Skill Feat)
Cognitive Mutagen (Item; +2-5; 1 min to 1 hour)
Choker of Elocution (Item; +2 or +4)
Stealth
Face in the Crowd (Conditional; +2; To go unnoticed in a crowd of similar creatures only)
Quicksilver Mutagen (Item; +2-5; 1 min to 1 hour)
Shadow Rune (Item; +2 or +4; Constant)
Clandestine Cloak (Item; +2 or +4)
Cloak of Elvenkind (Item; +3 or +5)
Cloak of the Bat (Item; +2 to +4)
Electric Eelskin (Item; +3)
Survival
City Scavenger (Conditional; +1; Applies to Subsist in the Wild checks made in cities only; Goblin)
Winter Clothing (Item; +1; Survive in the Wild to endure cold only)
Compass (Item; +1; Navigate in areas with uniform magnetic fields only)
Fishing Tackle (Item; Expert +1; Fishing only)
Bullheaded Mutagen (Item; +2-5; 1 min to 1 hour based on item level.)
Coyote Cloak (Item; +2 or +4; Applies to Cover Tracks and Survive in the Wild)
Oathbow (Circumstance; +2; Applies to Track checks vs your sworn target)
Tracker’s Goggles (Item; +2 or +4; Applies to Sense Direction and Track checks only)
Thievery
Thieves’ Tools (Item; Expert +1, Master +2; Pick Locks and Disable Device only)
Knock (Conditional: +4; Open a door, lock, or container)
Quicksilver Mutagen (Item; +2-5; 1 min to 1 hour)
Ring of Maniacal Devices (Item; +3 or +5; Applies to Disable a Device checks only)
Skeleton Key (Item; +2 or +4; Applies to Pick a Lock checks only)
Any
Bit of Luck (Conditional; +1; Only triggers if a check is failed by 1)
Competitive Edge (Conditional; +1; Applies if DC is 11 higher than your bonus)
Guidance (Conditional; +1; Once per day per creature)
Heroism (Conditional; 3rd +1; 5th +2; 8th +3; 10min to a single creature)
Inspire Competence (Circumstance; +2; Aid Another using Perform)
Recall Knowledge
Lorekeeper’s Fortune (Fortune; Roll twice on a Seek or Recall Knowledge check)
Loremaster’s Recall (Fortune; Roll twice and take the higher result)
Cognitive Mutagen (Item; +2-5; 1 min to 1 hour)
Diadem of Intellect (Item; +3)
Possibility Tome (Item; +5; Requires activation to use, applies to one skill per day)
There may be more that I missed, but for now this is pretty comprehensive. One thing I noticed is that Mutagens grant a pretty significant bonus compared to most items, especially since you can craft them as needed rather than use permanent magic items. I also noticed that very few spells grant bonuses to any skills - incredibly few, in fact. Most sources of skill bonuses appear to be permanent magic items, and there are actually a lot of options available.
In the interest of my sleeping schedule and my sanity I will post this as-is and post further comments in the near future. But for now, enjoy.
An update about the format - I start with the name of the feat/item/spell, then the type of bonus, the bonus the item grants, and any limitations on what checks the bonus applies to. If the bonus comes from an ancestry, class, or skill feat, I say so at the end - if one is not listed then the bonus comes from either an item or a spell/power, though bonuses from spells and powers are exceedingly rare. If the bonus is based on quality of the item I list the quality before the bonus it grants, and in the case of magic items whose bonus increases with a higher-level version of the item I list the variation as "+X or +Y".
The Knowledge skills (Arcana, Nature, Occult, Religion, and Society) have far less options to improve their bonus, but in exchange there are a few items that specifically improve the Recall Knowledge action. This is likely used to limit bonus stacking for Rituals, if I had to make a guess.
And one more thing!
I find it strange that Physical Boost is the only variable skill bonus. Why is that the only thing which currently does not grant a flat bonus? I thought for sure there would be other such mechanics but was very surprised to find it was unique.