EnglishManInNY:

Www.sloancars.com always have a good selection of Porsches. 

I like this one myself a v clean 993 Turbo S

http://sloancars.com/4441/1997-993-twin-turbo-s-blackblack-12000-miles/

+1 Sloan has very good cars with low mileage.  The 964 Turbo S they have for sale is a great and rare 911 (and a good investment too, although I think their asking price is quite steep for that model).

1994 964 Turbo S “package car” Guards Red/black 9,163 miles