ad-aware, advanced windowscare, avast! 4 home, ccleaner, cleanup, regscrub, regseeker, spybot s&d, tcpoptimizer, treesize free, uptimer4
there is a free online test site called pcpitstop.com, pretty good site with lots of features. just ignore the adds to download their pay software. they give lots of advice and with a little research you will be able to fix the problem areas for free.
also free, highly recommend pc wizard 2008:
Since 1996 PC WIZARD is among the most advanced system information programs on the market. PC WIZARD 2008 is a powerful utility designed especially for detection of hardware, but also some more analysis. It’s able to identify a large scale of system components and supports the latest technologies and standards. This tool is periodically updated (usually once per month) in order to provide most accurate results.
PC WIZARD 2008 is also a utility designed to analyze and benchmark your computer system. It can analyze and benchmark many kinds of hardware, such as CPU performance, Cache performance, RAM performance, Hard Disk performance, CD/DVD-ROM performance, Removable/FLASH Media performance, Video performance, MP3 compression performance.