There are ways to play with a keyboard that actually aren't horrible. I actually prefer a HitBox-setup on a keyboard(that is, using Space as the Up-key) above a regular pad.
That, or a controller converter for a Xbox/PS3-pad doesn't cost much afaik.
I don't play that much SF4 myself though(prefer TTT2 and SFxT), and I'm fairly bad at it. I also get framedrops and stuff on PC. :V
Perhaps that would work, but after so many hours behind a xbox playing all kinds of fighting games I think I'm just to used to it to change.

I never got a chance to play TTT2 (tho the first one makes me very nostalgic) or SFxT. I thought of getting the latter, but the animations just seem so... off. SF4's animation and movement looks so damn good, while everything looks a bit too flat for SFxT. I'll probably try to pick it up whenever the price drops though and I got time over.
Sadly, it often looks to me as if Street Fighter is the Starcraft of fighting game. As in it being many time more popular than other fighting games. So even though you could say that the fighting genre is still strong and point at SF, the rest of the current fighting games are a fair bit below.