Hit and Spell Hit rating is a crucial stat for any serious raider as it reduces the chance to miss with your attack. The following guide is to assist you in understanding the hit cap for both melee and spellcasters depending on class and talent specs:


Spell Hit

26.232 HR is worth 1% Hit
Initial spell hit is 17%, which is 446 HR.

This drops to 14% (368) with 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. It works out to be 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

That goes down to 5% (164) with specific talents below:
Death Knights: 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 Shaman with 3/3 in Dual Wield Specialisation.
1% (33) for Enhancement Shaman 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 guide will come in handy for you raiders, and eliminate any confusion over hit caps.