Mplayer will allow you to play movies via USB as well. I load up a USB flash drive (no matter the size w00t!), plug it into the back, load up Mplayer, and bam... my movie collection is ready to rawk. (external HDs work WONDERS for this one)
I don't know if there's a DVD/DivX player or not, but thats not a hard task to find out.