I have only two lenses, a Pentax kit wide lens (27-50mm eq) and a Sigma APO DG (70-300mm eq). Of these I like the Sigma a lot, it has a "macro" switch that lets me take shots up to 1:2 scale, and it has very good definition for its class - altogether quite a lot of bang for the buck.
I only have three, but my favorite to mess with at the moment is a tiny Rikenon P 1:17 50mm... I love what I can do with the aperture and it's little and not clunky to haul around (still manages to weigh more than the kit lens I have for my Canon Rebel, which is twice this little lens' size)
Very arbitrary lens, I know, but my grandma sent me her ancient camera with two lenses and hey... an adapter ring does the job and now I have more than just my kit lens!
I'm just a kid hobbyist, so... my stuff is by no means special. xD But there's my two bits.