A list of spells you want to have as scrolls as well as prepared is really useful. Spells like the above mentioned wind wall really don't come up every session, but when they do can make encounters significantly easier.
Haste (3rd level) is a spell that I'd suggest anyone have, if they can get it.
Fireball (3rd level) is often underwhelming, but if you can spare a slot for it, it has its moments of glory. Don't expect it to be useful every fight, but it is one of the best mook killers of its level. Also, Long range (400+40/level) Minimum 600'. Ever had a boss fleeing the scene? Here's your solution to put the last 20 point of damage on him. How about all those ship battles? Fireball may not kill the captain, but it's a 40' Explosion of fire in their rigging. 1 spell and they're dead in the water, with a burning ship.
Fly (3rd level) is an awesome spell. Difficult terrain means nothing to the subject of this spell, whether its yourself, the fighter in full plate, or that rogue/ranger who just wants to get in position. Also, great for ranged attackers & killing flying opponents.
Glitter Dust (2nd level) Once you can get it, do so. It's a 10' explosion will save vs blindness. Wont last long, but everyone who makes attack rolls will love you if it works, the rogue may even kiss you.
Also: once it is cast all invisibility within the radius is ruined, and any stealth checks take a -40. Solves a whole mess of problems
Invisibility Spells (1st-4th) These spells are game changers. Most of them require you to remain at most indirectly violent, but they allow free movement, and at least once much enhanced attack. Rogues may love you for this spell, but I find that a passive cleric/oracle/wizard is the best target. If they spend their time healing & summoning then they can now do this all fight long without being targeted.
Phantom steed (3rd level) Ever had mobility problems on your wizard? Ever thought you might? Think again with this spell!
Arcane sight (3rd level) See Magical auras at up to 120'. Make a spell craft check on any active spell you see, spend a standard action to tell is someone can cast spells, or is the simple old beggar they appear to be. Someone Invisible/stealthed? If they have a magical effect on them, they are now glowing (Note: Full concealment will still apply for invisible creatures!)
Also identifies magical items as per a detect magic.
Create pit Spells (2nd-5th?)
Save or be removed from combat, higher level spells are harder to escape from, and cause more pain. Note: These spells also create a 5' ring around them. Ending your turn on the edge of a pit, you must save or fall in. (With a +2 bonus.)
Grease (1st) Never gets old. Save of fall prone (major melee advantage), makes difficult, movement hampering space. Or cast on an item for reflex save or drop it. (Note: Clerics suck at ref saves, and need their holy symbols) Or cast on someone's armor / clothing to get a +10 CMD vs grapples and a +10 to escape grapples.
Magic Missile (1st) Direct Damage, with very little to be done about it. best uses: Wand of magic missile with your 1st 2 PA, now your wizard can always do something, and saves your spell slots for interesting spells.
Note: also a great spell to ready vs another spell caster. they cast a spell, you magic missile, assuming they don't have shield up, chances are they just lost their spell. Worst case, you delt them damage anyway.
Scorching Ray (2nd) If you want Direct Damage that scales well, scorching ray is a good call. Will loose usefulness later on, but for a 2nd level spell, being able to shoot 4/8/12d6 of fire on a touch attack, no save, isn't a bad thing to have around. especially in the mid levels.
Summon monster/nature's ally (1st-9th) WIN. Such epic win. No save, No SR (though protection/circle vs alignment can protect a creature) The early levels of these spells are underwhelming, but at spell level 3+, they can really shine. You get a Miniature Paladin, it takes hits for you, takes up space to help you control the battle field, it attacks for you, and can smite. Every time an enemy attacks it instead of an ally, they spell was worth it.
These are personal favorites, and mostly Arcane caster focused. Hope it helps!
A good rule of thumb: Any spell you pick should either have multiple uses, be especially good at what it does, or have fewer chances to fail (eg. Attack rolls, Save negates, spell resistance, energy resistance, creature type immunities. etc)