For those in the UK that feel the factory standard exhaust is a little too subdued, Hayward and Scott do a superb "bypass" modification which replicates the factory switchable sports exhaust tone -
Porsche 996 and 987 Boxster Stainless Steel Exhausts - Hayward and Scott
You can either drive your car to them and have your existing backbox modified or send them another backbox (like I did) and they mod. it and send it back in a few days ready to be fitted. That way you get to keep the original just in case you or the next owner don't like the finished result! The sound is gorgeous, rich and rumbly but no resonance or droning at cruising speeds. Really reasonable cost as well compared to other sports exhaust options.
Threaded Mode
