Here's a few that I've found:
Lindsey Racing do one that has a sort of upward bulge (not sure I like this one, but it's designed to fit a bigger intercooler).
Link
No idea where this one's from, the car's Swedish.
All Porsche Racing do a nice looking one, similar to what Paul posted.
Link
This one's from Automotion; looks nice.
Link
There are people doing these in the UK, too. Design 911 sell this one, but it looks like the Lindsey Racing part to me.
Link
Here's the Teilecar one that started this thread off.
Link
Teilecar also do a single-vent version, but it incorporates a headlight delete, so is for race cars only.
Deutsche Nine used to sell one that looked really nice, but I can't find it for sale any more.
GT Racing do a few options. Their catalogue is only online as a PDF to download:
PDF link.