One of the first questions to ask is what informs our gaming model of the races? Is the goal to:
1. Be true to "historical" D&D and fantasy writing?
2. "Re-envision" them?
Since Pathfinder is about back compatibility, I'm going to address the subject of racial ability scores from the perspective of #1. If we want to 're-envision' orcs, elves, etc. then it's a different ball game.
A History of the Races
Obviously, most of the races came to D&D via Tolkien. Since then, game editions and D&D fiction have enshrined certain aspects about them. Let's take a look.
AD&D 1e Racial Ability Scores (PH) - using the male scores only
Dwarf: STR 8-18, INT 3-18, WIS 3-18, DEX 3-17, CON 12-19, CHA 3-16
Elf: STR 3-18, INT 8-18, WIS 3-18, DEX 7-19, CON 6-18, CHA 8-18
Gnome: STR 6-18, INT 7-18, WIS 3-18, DEX 3-18, CON 8-18, CHA 3-18
Half-elf: STR 3-18, INT 4-18, WIS 3-18, DEX 6-18, CON 6-18, CHA 3-18
Halfling: STR 6-17, INT 6-18, WIS 3-17, DEX 8-18, CON 10-19, CHA 3-18
Half-Orc: STR 6-18, INT 3-17, WIS 3-14, DEX 3-17, CON 13-19, CHA 3-12
D&D 2e Racial Ability Scores (PH, PHBR8, PHBR10)
Dwarf: +1 Constitution; -1 Charisma
Elf: +1 Dexterity; -1 Constitution
Elf, grey: +1 Dexterity; +2 Intelligence; -2 Constitution; -1 Strength
Elf, sylvan: +1 Strength; +1 Dexterity; -1 Constitution; -1 Charisma
Gnome: +1 Intelligence; -1 Wisdom
Halfling: +1 Dexterity; -1 Strength
Half-elf: None
Half-orc: +1 Strength, +1 Constitution; -2 Charisma
D&D 3e Racial Ability Scores
Dwarf: +2 Constitution, -2 Charisma
Elf: +2 Dexterity, -2 Constitution
Gnome: +2 Constitution, -2 Strength
Half-elf: None
Half-orc: +2 Strength, -2 Intelligence, -2 Charisma
Halfling: +2 Dexterity, -2 Strength
Pathfinder Beta 2 Proposed
Dwarf: +2 Constitution, +2 Wisdom, –2 Charisma
Elf: +2 Dexterity, +2 Intelligence, –2 Constitution
Gnome: +2 Constitution, +2 Charisma, –2 Strength
Half-Orc: +2 Strength, +2 Wisdom, –2 Intelligence
Halfling: +2 Dexterity, +2 Intelligence, –2 Strength
My Analysis
I don't really think much about the "artifical balance" of one physical and one mental bonus whether they're merited or not.
Dwarves - consistently over time, +CON, -CHA. I see no grounds for the +WIS, however, as D&D and Tolkien dwarves have been beset by greed, hot-headedness, and other "low Wis" issues. I say +2 CON, -2 CHA, and cool racial abilities fill it out.
Elves - Well, there's the bow elf vs magic elf divide that started with sylvan/grey in 2e and led to this 4e abomination of elves vs eladrin. +DEX, -CON is consistent over time. Maybe let them choose +2 INT or CHA (smart or pretty)? May help take the place of the cut "prettier than you" racial ability.
Gnome - Hmmm. In 1e, smart and fairly tough and strong. In 2e, smart and not so wise. In 3e, tough and weak. A strange mix. I would tend to try to make them distinct from dwarves and halflings - gnomes are small but legend has them being fairly warriorey and of course in D&D, illusioney. The CHA bonus comes from nowhere. I'd go with +2 CON, +2 INT, choose -2 WIS or -2 STR, though neither's that well merited - you could just nerf the rest of their racial abilities.
Halfling - Always dextrous, with a side of tough but weak and not wise. DEX +2 and STR -2 are clear. The INT bonus comes from nowhere, and I find this one the most offensive of the various mods - halflings have never ever been portrayed as good wizards. Small, +DEX, and +INT makes them min-maxed for wizardry. And even when halflings have been depicted as "clever" it is more the wily-clever of WIS and not the book-smarts of INT. +2 DEX, -2 STR, and +2 CON, then drop the luck racial. (1e halflings were CON up to 19! And Frodo took a lickin and kept on tickin.)
Half-orc - from the beginning were more CON than STR until 3e. The WIS bonus is only marginally less awful than the halfling +INT. And unless you're changing the orc stats too, it makes no sense - Str 17, Dex 11, Con 12, Int 8, Wis 7, Cha 6. Make half-orcs CON +2, STR +2, and up to all of INT, WIS, CHA -2 - or really, they have suck for racial abilities otherwise, +STR +CON -INT is balanced.