Wow, I wish I had asked here before I bought, that's a great deal on wheels! I just picked up some used hollow spoke turbo twists, very light and about the same price, but I like the size of those wheels better. Darnit!
My '03 996 is running the exact same tires as your car, I've been buying 997/Cayman take off tires. Until recently I've been running the Michelin Pilot Sport PS2, which is what you have, and I got tired of buying new sets after I damaged them with autocrossing. I find the PS2s to be great, but very susceptible to damage when you push them hard. I've destroyed 5 tires (3 front, 2 rear) in 1 year!
If you want to stay in street stock, you can't go with the R888s. I asked this same question recently on Rennlist, you can see the thread here:
http://forums.rennlist.com/rennforums/s ... p?t=409872
I chose Falken Azenis, which seem to have a very good rep for autocrossing, and are very well priced. A full set cost me $724 delivered (225 front, 265 rear). DiscountTireDirect.com (which is different than DiscountTire.com!!!). I've had the wheels and tires on the car for 1 day, and have not yet tracked it, but so far the tires have impressed the hell out of me. And they are 200 treadwear, so they are fine for street stock. I'm considering putting on a set for daily driving!
I saw an ad for local pickup of some OEM turbo twists for $500 recently. You can definitely get a set of OEM wheels for under $1000 (I paid $850 for my hollow spoke turbo twists) if you take your time and look around. The wheels Dave just mentioned look very good, and I might have gone that way if I have known about it sooner. To keep it simple, I would just look around for any OEM wheel that has the same size as what you have on now (18x8, 18x10, and match your current offsets +/- 10ish). If you are unsure, you can always post a question here or at Rennlist about whether a particular wheel would fit, and you'll usually get an answer in an hour or less.
Here are the places I look at for used stuff:
http://forums.rennlist.com/rennforums/f ... .php?f=136
http://ad2ad.com/?portalid=1001103
http://www.6speedonline.com/forums/foru ... y.php?f=67
http://forums.pelicanparts.com/forumdisplay.php?f=17
Irksome, aka Tom, aka 1414