I really love a parti-coloured dog. Brown/white and red/white are, for whatever reason, favourites. I don't usually like all-white dogs but dr2little's Sophie is my favourite dog on Chaz solely because of her colouring (that white against her nose is just awesome looking and I think her coat texture has something to do with it as well).
I'm not too big a fan of all black dogs. I like them, just not a favourite.
Merle is definitely a breed to breed thing. I love it on BC's and Beaucerons but in other breeds, like the Dachshund, I am only a big fan if it's a longhaired.