Juno. Simple interface have everything, jobs a goodun. Juno player also good now.
Red-Eye Records. Just great for dubstep.
Trackitdown - Nice interface, stupid way of grouping by track rather than release though.
Boomkat, great review system, horrible player and organisation of tracks and genres.

DJ Downloads - Really good interface, high quality audio and you can scoot through the whole of a tune rather than crappy 30 second clips.
Probably the best place asthetically, but doesn`t seem to sell enough or get enough attention.

Beatport sucketh in every way. Pay your way into the charts system, horrible interface, take the highest chunk away from artists, full of crap music.