Other 303 Emulations (Score 1)

It's not free, but I wanted to toss out AudioRealism Bassline as another great 303 emulation, which I generally prefer to Rebirth -- it has a larger interface, and more importantly it's a standard VST so it integrates easily with whatever production/DAW software you happen to be using (it sounds great too).

I'm still pretty interested in Rebirth for the 808/909 emulations, though; I haven't seen any other program that does as good a job reproducing the tweakability of those drum boxes.

Also am way excited about the rerelease of Rubber Duck -- to this day, it remains one of the best-sounding software synths I've heard.