I have several different viewers on my machine. I never use Quicktime... just don't seem to need it for anything. LOL

For .AVI's I would have to suggest either Real Player (available at www.real.com) or WinAmp (www.winamp.com). Both have free versions and have worked very well for me. Another option if using Windows Media Player. I like the library feature and the fact that (with my .mp3s) it will search the internet to find the exact song title, artist name, album, genre and year of release for me. You even get little thumbnails of the album covers that show up if you're using the icon view for your music folders.

One problem I've had with the Real Player is it wants to lock up sometimes. For this reason I don't mess around with it much when it's onscreen. Just let it pop up when you select a song/video to play and watch. The more buttons you push the more likely it is to lock up. But you get nice quality playback with it (even on cruddy laptop speakers).

Hope this helps.