WinDirStat is a great hard drive usage visualization tool that helps you identify and clean hard drive space issues. If you are running low on disk space or just want a cleaner system, this tool will provide a visual of what is hogging up your precious space.
Belarc Advisor is a great free tool for computer auditing and software asset management. It helps IT professionals and consumers attain a comprehensive hardware and software inventory on their computers. Belarc is also handy in recovering lost software keys.
Download here: http://www.belarc.com/free_download.html