In order of smiles / pound on my little 748...
Magnesium wheel
Slipper Clutch
Suspension (Fork rebuild / springs / revalve, Ohlins rear Matris Steering Damper)
SPS Conversion (Heads, pistons, cams, cam timing, Dyno setup etc)
The next mod's I make will most likely be to my riding by re-visiting CSS etc.
Jason