I've never got a virus yet from Grokster (spyware-free version available at
Cleanclients).
(Grokster accesses FastTrack, the same network as Kazaa & iMesh, so you'd be able to d/l files from users of those progs too.)
It also has a built-in filter to avoid possible virus files (.vbs, .exe etc.) if you so choose. (Tools > Options > Filter). Also has a block list, you can add suspicious words/extensions to it.
More filtering options possible using the add-on program
PseudoTrack.