The n810 resistive touchscreen (best ever) w/ multi-touch
The n810 stand (best ever)
The n800 hardware keyboard: NONE (best ever)
The n900 stylus and stylus location (best ever)
Besides keyboard, no deletions of n900 hardware capabilities
Compass
D-Pad
Multi-core CPU (Medfield would be a bonus)
Hot swappable battery with offline charger, using AC adapter if necessary
MeeGo

And most importantly, a developer discount program