Random post, but I figured that there is a great deal of open source software out there that is becoming more and more polished so I thought I'd put up some of my Favs.

-Scribus: Desktop publishing really really handy
-Eclipse: Heavy duty IDE
-Gretl: Econometrics tool but really handy for stats analysis
-Jmeter: Load Testing - come a really long way
-LoadUI: Just starting to look at this for load testing too
-SoapUI: Webservices development/testing/everything
-GIMP: Image editing. A little esoteric in terms of interface but heaps of help out there