I've had some great success with some recent Futurama episodes.
These were already in DivX .avi when I reencoded them for the 6k, but I'd think you could start from any type of file.
Using Quicktime 7, I went into "Movie Properties," selected the video track, and rotated clockwise using the curved arrow button. Simple, though this didn't work for me using the same process in Quicktime 6.
I then exported the file using the latest DivX codec. 1:1 ratio, 540x480 (or that ballpark), 15fps, 450kbps, Better Quality, 2-pass encoding, with an MP3 audio track @ 64kbps/mono. That gave me an 80MB file of a 20-minute episode that played very, very well, though it still chokes a bit during the title sequence (blazingly fast, if you know Futurama). I'm sure by adjusting the keyframe and modulation sliders, I could tweak a bit more performance out of it.
I'm using the bleeding-edge version of
zplayer (which trumps Kino), and using the following mplayer settings: -really-quiet -framedrop -cache 2048 -vo fbdev -fs
In any case, this gets a bit more use out of the 6k's beautiful screen, and has dazzled some casual onlookers.