[["MPlayer"] http://www.mplayerhq.hu] is a powerful Multimedia player and more. - It plays almost anything from RealPlayer to avi, but has licencing problems which makes it currently unsuited for going into Debian/main.

Building your own package by yourself for Debian is easy, though, and if you're really lazy precompiled debs are available for x86 and ppc at [http://marillat.free.fr/ http://marillat.free.fr/].