These days finding fan albums for free seems to be a rarity. However, I did come across three very interesting doujin game albums and the creators have been more than happy to offer them to the game music-loving public for, you guessed it, free.
Castlevania SOTN has, in my opinion some of the best fan-made arrangements for one of the greatest soundtracks in the series (Bear in mind that Castlevania music in general is awesome). I figure just about everyone has played SOTN so it shouldn't be too hard to recognize what tracks are remixes of what. The whole album is gold but my pesonal favorite track is "Illusion Hop," which is a remix of "Dance of Illisions." (The track plays when Richter fights Dracula at the beginning of the game.)
Anyone that owned a Nintendo 64 has undoubtedly played GoldenEye 007. A group of hardcore fans got together and created an updated version of GoldenEye using a Half-Life mod. The visuals have been updated and so has the soundtrack. The tracks don't do too much diviating from the original source but what remixing there is is quite good and the revamping is very impressive.
If you haven't played Battle Garegga, or have at least heard the soundtrack, it may be a bit harder to appreciate Battle Garegga Anthology. For the uninitiated, Battle Garegga is an arcade shoot 'em up and a pretty intense one at that. If you game on MAME, I recommend trying it out. Anyhoo, the arrange tracks presented here are pretty polished. How this album only got ranked three and a half stars at VGMdb.net is beyond me.