Exhausts?

[marty55]

have a look at twin loop exhausts.
Mugen have a nice one out. supposed to be quite good.

[starboyftp]

Check out an exhaust from RS-R. They have a system called the EX-Mag if you're looking for something that gives decent gains but still remains relatively quiet. The website quotes about a 10HP and 10lb-ft increase in power. Although it's relatively expensive. About $600 USD, but probably worth it if you want something nice.

[crx92ie]

That's probably an optimistic claim for gains from purely changing the exhaust.