I like so many, it's hard to say. I've always liked music videos of CCS, centered around the beloved couple; Sakura and Syaoran like for example, one AMV with the song " Butterfly " or something like that from DDR -- love it. ^__^; Or just about any S+S AMV is decent.
But there is another AMV that I like of RahXephon. Even though I haven't exactly seen the anime yet, the AMV was well done. The music choosen for the video suit it perfectly; and it contain a nice beat. It's fun to listen to. I can't think of any others.. Oh well. ^^;;