If you're new to open source, finding recommendations of solid open source software to try can be difficult. This is particularly the case on Microsoft Windows, whose user communities tend to be less open source aware than Linux or MacOSX user communities. Here are some starters for finding open source to try:
http://www.opensourcewindows.org/ Recommendations desktop software for windows.
http://www.osalt.com/ Listings of specific proprietary software packages and their open source alternatives. Lists both desktop and server software.
http://www.openadvantage.org/articles/oadocument.2005-04-19.0329097790 a somewhat dated guide to choosing an open source CMS (Content Management System) from OpenAdvantage
Choosing a Linux Distribution a guide from OSS Watch