So what does the FOSS crowd suggest? Theora, a codec that isn't even out of alpha. I can't speak for anyone else, but last I knew "alpha" meant "for early testing only, may be extremely buggy and fail in bad ways".
Personally, I'd recomment RealPlayer. They're the only one who've actually got the whole thing of *streaming* video right, and as a bonus it runs under all major systems.
