this is really going to depend on what you like to drink, but I bought bulk from hopsdirect.com and selected Cascade, Chinook, Fuggles, Northern Brewer, and EK Goldings.
The chinook is one I like to bitter many things with.
I use the NB and Cascade in my IPA.
I use the fuggles and goldings in mosy of my english style ales (porter, brown, esb, etc)
I bought mine from hopsdirect.com, which I think is a better deal freshops b/c hopsdirect sends you WAY more than you actually order... each 'pound' ordered weighed about 1.5 pounds on the scale.
-walker