I swear by MoboPlayer as well, though sometimes I drop back to RockPlayer Lite just to see how it handles things. Love how Mobo remembers where you've left off regardless of how many movies/videos you've watched in between.
On the other side of the spectrum is mVideoPlayer, it has an awesome interface but only supports stock Xoom codecs. They recently updated to support sub/idx support for subs, but that whole stock codec only support kind of ruins it for me. I use this for any YouTube videos pulled w/ TubeMate.
I tested QQPlayer as well, it's not too bad but I was really searching for subtitle support so I could enjoy foreign flicks on the road. It didn't really offer much aside from srt support, but I figure I'll keep it in the hopes it'll see more development in terms of sub support (I believe it's developed in China or Korea, so sub support would have a higher priority).