I've seen pretty much every combo often enough to not be impressed by it anymore, or do a double take. Looking at my Fem Pandaren Warrior is pleasing and new enough to make me consiously watch though.
worgen warlock/rouge/death knight.
dwarf warrior (thank you J.R Tolken).
NElf female has to be the most underrated race/gender in the game. They look ugly until you get them in higher-level gear, though.
Same goes for Draenei Males. They look horrible until they have some real shoulderpads on.
The Book of Ghost Crab:
And he led them out until [they were] over against Orgrimmar: and he lifted up his hands, and buffed their classes. And it came to pass, while he buffed their classes, he parted from them, and was carried up into the Emerald Dream. And they worshipped him, and returned to the General Forums with great joy.