Now that I have used the device for a few days:
Landscape e-ink (previously mentioned)
BT Keyboard would be nice
Better LCD Screen. I would like something like the iphone/ipad yes you would lose the ability to use a stylus on that side but the screens are so much more responsive (Yes I am willing to pay more)
Better power management (Windows like true hibernation)
Turn of Scroll Wheel LED (Drives me nuts!)
Smooth Case with better grip Metal case option
Smaller bezel with larger screens or smaller device
Faster processor - Generally works good until you browse the image gallery and a few other more intensive apps
Marketplace (I know they are working on this)
Additional UI enhancements and latest version of Android

Stuff still to try and comment on:
USB Flash drive
External Keyboard