Short of gutting the car into a metal shell... ways of reducing weight are:

- light non-motorized seats
- non electrical windows
- no subwoofers - or non stereo better
- no PCM GSM nonsense
- non electrical sunroof or no sunroof
- no back seats (a la GT3)
- no console

If you think about it you could probably order a car pretty much like that w/ a few exceptions.

But... I noticed that many who complain about weight go ahead and add all kinds of junk on the exterior (aero kits and such), and larger/heavier 19" rims, adding more weight. Go figure.