Aerodynamic Awesomeness: Upgrades to Improve a 930's Downforce

As many of us know, the 930's stock aero package is somewhat lacking in terms of downforce. I'm looking to upgrade various components to significantly improve my car's grip and overall driving experience. Specifically, I'd like to hear about upgrades for front splitters, rear spoilers, and diffusers that have been tested on actual track days or spirited street driving.