Leo,
To add to Simons list I've done the following:
Touring screen and Touratech extension.
Home made front fender xtenda...keeps all the crap off the front of the engine.
Headlight cover.
Garmin GPS III and Touratech bracket.
Hand guards.
H&B engine bars.
Touratech side panels.
Rear hugger.
BMW panniers and rails, Givi topbox.
Press to talk switch for bike to bike radio with my mate.
BMW tank bag (will replace at later date with Touratech)
Remus exhaust system (ditched cat).
BBpower chip.
Am in the process of replacing front brake lines with braided stainless. After that it's 35mm bar risers, centre stand bash plate, sidestand footplate. Over the winter I'll have the sump bashplate drilled and polished. Then I might add a few of the decorative goodies from the Wunderlich catalogue such as the oil cooler grill.
You are only limited by the depth of your wallet!
-----
Mike