I love cover songs, especially where the song is totally transformed by another artist (like the Dickies or Tori Amos are wont to do). Have you ever wondered what songs by an artist have been covered, or what songs an artist has covered? Check out The Covers Project, which aims to build a database of cover songs and create cover "chains" (A cover chain is a set of songs in which each song is a cover of a song by the band who covered the preceding song). You might be surprised who your favorite artist has covered (or been covered by).
Another cover item: have you ever looked for a piece of CD cover artwork? Try CDcovers.cc, the self-proclaimed "world's largest cover archive." Not only audio CD artwork, but also Playstation, Dreamcast, DVD, Gameboy Advance, etc. This site is perfect if you lose that CD case (or misplace it, like I often do).