Further to what I suggested earlier, the route I chose for a cost/performance basis was QA-1 (Carerra) coil overs from Summit Racing. Weigh your car to determine spring rates using the formula supplied by QA-1.
http://store.summitracing.com/partdetail.asp?autofilter=1&part=HAL-DDR4855B&N=700+400026+4294848303+4294908350+115&autoview=sku
Also available in single adjustable and/or poly bushed
Springs are cheap and it is easy to change the spring rate. If you get it right on an IRS car you may not need a rear sway bar.
Changing the ride height is a simple matter of winding the spring up/down so buy the adjusting wrench and bearing spring plates to make the job even easier.
Red 9 is nice stuff but check out Eagle Performance
http://www.eagleperformance.com/CoilOverKits.html
He can supply the conversion kit for 944 trailing arms to the Beetle torsion tube as well. I chose to weld and bolt them in place but maybe overkill.
My CMC sub frame did not have clearance for the spring, so I had to modify it and at the same time incorporated Joe's saggy bum fix.
+2 on QA1s. I have them on my Vintage Spyder, as does LennyC. Vintage SPyders are set up with coilovers from day 1. We both had Aldans and I would NOT recommend them, basically drag-race shocks, where you want weight transfer. But the Qa1 double-adjustables are well, excellent. Nice firm or comfortable ride, your choice with the turn of a knob. Lots of circle-track and road race guys use them.