Ed Eubanks over at Low End Mac has a nice set of suggestions for optimizing performance on your Mac. The main upshot of the article is to turn off or delete things you don't need (e.g. Universal Access, seldom used System Preferences, extra localization languages, etc.) in order to salvage as much RAM and hard drive space as possible, but he has a variety of good suggestions. Their motto over there is "How much Mac do you need?", but even if you've got an Intel beast I've found that you pretty much never have enough system resources, so these are good tips for everyone. Check it out over at Low End Mac.