I was browsing online for a free audio converter and ran into this site, 51 Essential Programs For A Freeware Only PC at www.freewaremission.com. This page was published almost a year ago, but most links are still working. Here you can find media editors, partitioning utilities, anti-virus programs, and drive cleaners, all free!
Free software is great, and there are quality open-source tools out there, but always be cautious installing any software you're unfamiliar with to your PC, especially if you run a home network. Viruses and other mal-ware programs are often packaged as legit products.
Whenever I find free tools, I usually go to www.cnet.com and search for a review of the product before installing. CNet's reviews are very reliable and CNet also provides safer links for downloading free software.