I'd like Draenei rogues and warlocks, though it doesn't make a lick of sense lorewise, i think Blizz should just go all-out with the "Gameplay over lore details" thing by now at least where character class is concerned, in any realistic society there would be individuals who deviated from societal norm and went with the unaccepted lifestyles (or class) of their respective societies...
Pandaren Druid just so i can be a REAL big fluffy panda.
Blood Elf druids and Tauren Rogues.
when all else fails, read the STICKIES.
Undead paladin and Draenei warlock are the only combos I really wish where there.