I've been blown away by RockPlayer these past couple weeks.
http://www.diffthink.com/forum/viewtopic.php?f=2&t=4

It's the only player I've seen on any mobile platform of note that can play Divx, AVI and MP4 video all at once. Nothing on the iphone can do this, period.

This isn't a big deal to most consumer users but it's a godsend for those of us that have ripped our DVD collections or download things off the torrent networks. Now you can simply copy files over rather than worry about transcoding and format.

This, with a 32GB microSDHC card, is HEAVEN on long trips now and one of the key "little things" that has made me turn away entirely from the iphone platform. It's unlikely Apple will ever support Divx (at least not in the next year or two), so this saves me many hours of frustrating one-off transcodes.