I'd think about adding a 512MB chip as an economical solution that will give OS X enough to do most things without excessive disk swapping. Macintouch recommends Ramjet RAM based on reader reports, and I've had excellent luck with their RAM myself. I would avoid bundled RAM from places such as MacWarehouse; you may not know what you're getting, and as others have said, you don't want low quality RAM. Apple's RAM prices are insane, but be prepared to remove any third party RAM if you want Apple to help troubleshoot or repair problems.
