The Cayman S has twin tailpipes, while the non-S Cayman has a single pipe. The standard wheels (17" vs. 18") are obviously different, although you can get the non-S Cayman with 18" or 19" as an option.

__________________
John
'07 Cayman S
'89 944 Turbo - sold
'05 Saab 9-5 Aero