I pretty much always use liquid yeast (dry is fine, not trying to start that argument), and I pretty much only keep a couple around.
I use White Labs American Ale yeast as my staple. I use it for everything from a light blond, to a ESB, to an IPA to a Stout.
I also keep on hand White Labs WLP300 Hefe yeast on hand for all of my wheat beers. Hefe's, american wheats, fruit wheats, whatever.
I also keep on hand WLP570 Belgian Golden Ale Yeast. I use this for all my Belgains, whether it be Golden Ales, Dubbles, Tripples whatever. However, I am considering changing this. I am going to try a different Belgian yeast this summer and see if I like it better. This yeast has a wonderfully complex flavor/aroma, but it can be a PITA as it is a sloooowww fermenter and flocculation is pretty bad. With this yeast I have to give it a long fermentation, and a long cold crash before I can keg it and even after a cold crash, I still get the occasional pint of yeast. I think I might try the blend WLP575 and see what I think of it.
And that is pretty much all I will use all summer. This winter with a colder basement, i tried a couple new yeasts that I just about fell in love with.
Wyeast 2112 California lager. Fermented great in my 58 degree basement and was very clean yeast. Malt/hop profiles really shined with this yeast.
German Ale 1007. This is probably my favorite yeast as of right now. At the low end of the temp range (58) where I was fermenting, it fermented very, very clean. Almost lager-esque, so much so that I would have no problem making an Okoberfest, or Bock or some other sort of lager like that. I dont think I could make the American Lager style with it, it is not quite THAT clean, but it is a very clean, very active, very good yeast at that temp.