Sienna Stow-and-Go Seating. They should make the full-flat stow-and-go seating like the Dodge/Chrysler have. I've seen that and it's actually very nice. It does make the seats smaller and less cushy, but then you have a massive amount of flat-floor storage and that's very impressive overall.
Otherwise, typical options are very important from the backup cameras and sensors, a good stereo and entertainment system, built-in DVD is pretty cool and a must-have in my opinion.