UseTheSource has compiled some interesting statistics as to the popularity of various languages in open-source development, using Freshmeat and Sourceforge as the, uh, sources for his stats.

See the Freshmeat statistics here, and the Sourceforge statistics here.

No real surprises here. C, C++, and Perl are all very big. Python is number six in both lists. VB is nowhere, whereas I think that in the commercial world, VB is big. But then, surely no one uses VB by choice, and contribution to OSS projects is usually voluntary.