Try www.downloads.com is also a good place to start, most of them are free and open source. If you're using Ubuntu Linux then is a place to check out. On a debian Linux you can also find great software in the Synaptic Package manager (System -> Administration -> Synaptic Package manager or command line: sudo apt-get install what_you_want_to_install). Unfortunately most of the time it's just knowing where the best software is.