Any tracker with 8bit soundbanks.

FruityLoops has a very nice NES soundbank, if I remember correctly, although I'm not a huge fan of FL. Offically, FL isn't free, but hey, we're on the internets. There are good trackers (ie Modplug Tracker), for which you can probably find "chiptune" samples too.

Of course you're not really programming said chips to make your very own sound, but that will be enough in most of the cases you'd encounter.