Well, actually not only for them, and also not only limited at chiptunes, but anyway, great news.
KVR Developer Challenge got some serious names to produce some software and put it for free.
One good library sampled directly from 3 different versions of the Commodore 64 is a collaborative project between Bedroom Producers Blog and Rhythmic Robot.
The library is 30 multi-sampled instrument patches (Kontakt 4 + SFZ + Zampler).
So, if you don't have Kontakt, grab SFZ Player or Zampler (both free, so no 15 minutes Kontakt Player limitations).
Be sure you'll vote for your favorite pieces of software and grab the freebie while is still hot: