As a side note, and to be pedantic, QuickTime supports the AVI container just fine. It just doesn't support the DivX/XviD video codecs most often used in the AVi container these days (and neither does Windows, out of the box). Perian is your best bet for that.
VLC is nice for the occasional stuff that Perian still doesn't play, but I prefer to use QuickTime player as my primary, since it's better integrated into the system (what with being the system-wide media framework and all). 🙂