White Brothers carries progressive-rate springs for forks and shock. Others do too, but WB seems to be the one you hear about most. Contact a suspension shop who can tell you what's available. Also, there are quite a few exhaust upgrades out there--Pro Circuit, FMF, Cobra, and SuperTrapp among others. SuperTrapp has a great reputation. Just remember that if you're opening up your exhaust, you need to create more intake to maintain the balance--I'd recommend looking into re-jetting and install a K & N filter. The XRs respond well to K & Ns and they are super easy to take care of.