I have a fair few. Of all my consoles though the one I play the least would be my WonderSwan Color. I only have one game for it and it's in a language I can't yet understand. There aren't many games about for it that are in English and the ones that are can be pretty hard to find.
Others would be my Master System, NES, Mega Drive and Sega Saturn, and to a lesser extend my N64, SNES, Gamecube and Dreamcast. Can't find any MS, MD, NES or Saturn games I'm interested in, most N64/GCN/Dreamcast games I'd be interested in I already have on another console and most SNES games I'm interested didn't come out in PAL or are horrendously expensive here. Sigh sigh. Hopefully when I finally get an American SNES it'll get more love though.
Oh yeah, and my Wii. I could list the reasons all day.