Handbrake for conversion, MPlayer and (very infrequently) Quicktime with Perian for playback or VLC.

Any player that doesn't support two different skip amounts is next to useless for playback of anything you may need to rewind/forward. If a player doesn't have skip at all, like Quicktime, it's really the pits. After getting used to instant jumps, using an accelerated playback for seeking, even if progressive (like a DVD player), is as bad as getting teeth pulled.

It's interesting news about the new QT Player and lack of a paid Pro option - it was rumored long ago, but I haven't seen anyone else mention it since SL's release. I've always thought the $30 was an exreme gouge, especially considering you still had to pay even more for MPEG2.