Another good fan site: The Castlevania Dungeon. Try the 'Foriegn' or 'Wierdness' sections under some of the games. There's a nifty looking hidden game in PCE DracX, and a debug room available in PSX SotN with a GS code. Plus unused spite animations. eastereggs etc. There is some info about the DC version, although I can't find anything about the unreleased 32X Castlevania. I have seen what are supposed to be sprite animations somewhere, but I'm not sure if these were real or not. @ASSEMbler - look, CV for the Amiga too :ramen
Castlevania Dungeon is hosted by Classic Gaming... like another site I know of. Go to classic gaming and then look under their hosted sites. It is a great site for Castlevania info.