For "commercial" Amiga remixes, you might wanna try: Immortal 2 (remixes of game musics) Bjorn Lynne - Revive (remixes of his classic mods, including 12th warrior and Moongazer)
Both available at, for example, Lynne's online CD-shop: http://www.lynnemusic.com (clips available from both CDs)
For free C64 remixes, check: http://remix.kwed.org
