Only 2?... I'd have to break it into categories..
Safety:
1) HID upgrade & motolights... immediate difference was cars gave me more space instead of pulling out in front of me.
2) Autocom comms w. B/tooth module... easy & constant communication with whoever is on the back (my lady or one of my sons) and by phone
Comfort:
1) Rick Mayer recovered seat, go the distance without numb-bum
2) Grip puppies and throttle rocker OR Z-technik Vstream windshield OR MOPs for long distance
Performance:
1) Wilbers shocks f&r... what a difference
2) not really an upgrade but... fuel.. stay away from ethanol additive if possible, get the highest octane you can.
Fun stuff:
1) A decent GPS (Garmin 500/550) at the moment
2) GoPro for capturing the other f'wits on the road