Well I'm a good enough player in general that no champion is entirely unplayable for me but the ones I play regularly number in the 15-20 range I'd say? The ones I would never seriously touch at all are few and far between.
Ahri, Ashe, Cho'gath, Darius, Draven, Garen, Graves, Karthus, Kha'zix, Leona, Lulu, Malphite, Morgana, Nasus, Nocturne, Shen, Singed, GEMS, Varus. Dat's 19 champs. And I dunno there's maybe ten more or so that I didn't list that I used to play regularly and can play well, I simply don't anymore (like Alistar or GP). AD carry is basically the same regardless of which one you're playing, same with support, the ones I listed are simply my preferred ones. For some reason I keep trying to play Lee even though I'm not that good on him. I'll still play Blitz if he's open probaly, occasionally hit up Jayce or Elise or whatever as counterpicks (well Elise "counters" everything but whatever). Hecarim might make my list soon, he's really growing on me. Blah blah blah.