I ran up a small guide for my guild forums, and decided to repost it here too, with a few changes (Like making it less Alliance focused, adding classes we don't have). Searched for this and found a guide from TBC, but nothing WotLK related, or with enough clarity.
I've tried to keep this simple, and just list what you need for what class, with what buffs.
Spell hit:
26.232 HR is worth 1% Hit
Initial spell hit is 17%, which is 446 HR.
This drops to 14% (36with 3% talents, which most caster classes have, or 13% (342) for a Balance Druid with Balance of Power.
Mages: Arcane Focus, Precision.
Warlocks: Suppression.
Priests: Shadow Focus.
Shamans: Elemental Precision.
This drops again to 11% (289) with 3% hit raid buffs (Imp Faerie Fire from Balance Druids, and Misery from Shadow Priests).
This drops again to 10% (263) including the Draenei racial (Heroic Presence)
For Night Elf Balance Druids, who get a 4% talent instead of 3%, this means they only need 9% (236) to hit cap, if grouped with a Draenei, and specced into Imp FF.
Melee hit:
Melee's a little more complicated. There's 32.79 HR per 1% of hit.
Standard (White damage) melee single wield hit is 8% (263) (So 1h and shield, 2h)
Standard (White damage) melee dual wield hit is 28% (886) (2 1h, or DW 2h with Titans Grip)
However special attacks (Yellow damage) with dual wield, have only an 8% cap.
So:
Initial melee hit is 8% (263), both single and dual wield, for yellow damage
For Feral Druids (Cat/Bear), the hit cap is the full 8% (263), or 7% (230) with Heroic Presence.
That goes down to 5% (164) with certain class talents:
Death Knights (1h/DW weapons only): Nerves of Cold Steel.
Hunters: Focused Aim.
Warriors: Precision
That drops again to 4% (132) for all those classes with a Draenei in party.
With increased talents in other classes, we also have:
3% (99) for a Rogue with 5/5 Precision.
2% (66) For a Rogue with 5/5 Precision and a Draenei in party.
2% (66) For an Enhancement Shammy with 3/3 in Dual Wield Specialisation.
1% (33) for Enhancement Shammys with their own racial (Alliance only) and 3/3 Dual Wield Specialisation.
I've also been informed that a Rogues Poison's work from the spell cap. I've done a little research on this and it looks like Poisons need 14% (368HR), after accounting for 5/5 Precision, or 13% (342) after Heroic Presence. However similar to spellcasters, poisons will benefit from Misery/IFF, which will lower the poison cap to 11% (289) without Heroic Presence, and 10% (263) with a Draenei in party. Once a Rogue hits this, they'll be capped for both poisons and yellow damage, but white damage will still be uncapped, similar to most dual wield classes.
(Thanks to Dragaei, who let me know poisons used a separate amount.)
Hope this'll come in handy for some of you, and eliminate any confusion over hit caps.
Feel free to post, or PM me if you think I've made any mistakes and I'll correct them, or even if you just have something to add.