I just use msconfig to disable all of the processes that run automatically on startup except for my antivirus. A lot of registry cleaners and performance apps aren't very thorough, can damage the computer, or just suck memory themselves. It's hard to find freeware that isn't malicious itself. Also, if you have a lot of windows open all the time, keep them minimized and they will actually take less memory than if they are all open on top of each other. Some of my friends overclock their processors, but I don't know how.