I've been using the website "Alternativeto.net" for a while now. If I had to pick a social online feature I like, it would be an easy win - ahead of facebook, blogger, twitter etc. It's pretty simple. People add software entries and say what it's an alternative to. Other people then vote as to how good of an alternative it is.
As a result you've got a huge database of alternatives to many common/uncommon software packages.
Microsoft Office 365 is an annual Benjamin. Want an alternative to Microsoft Office - http://alternativeto.net/software/microsoft-office-suite/
The first 5 options presented are by alternativeto.net are free.
So many free options. Um - yay?
Well, that's a really common example - lets try some other options:
Notables: Gimp, Paint.net
Visual Studio: http://alternativeto.net/software/visual-studio/
Notables: Eclipse, NetBeans, Aptana Studio, CodeBlocks
Adobe Lightroom: http://alternativeto.net/software/adobe-lightroom/
Notables: Picassa, RawTherapee, UFRaw, Bibble
Notables: Notepad++, GVim, Sublime Text, SciTE,
Notables: Python, C#, Go
Notables: ZSNES, MESS, Snes9x ES
Notables: Google Voice and Video chat, ooVoo, Voxeet
Notables: Microsoft ICE, Photosynth, PTgui
Well the list goes on as you can see. Even more esoteric software, such as Super Nintendo emulators and Panoramic image creators were listed and had many options. This is great - since you can try as many free/trial options and just use the one that best fits your needs.