Why buy the cow...

Companies like Google and Microsoft give away free software as a courtesy to their users to hook more people on their services ("free as in beer.") But open source organizations are often non-profit and made up of volunteer developers who release free software because they believe users have a right to control their data ("free as in speech.")

I highly recommend 1-4, 6 and 9. Not that the others aren't good, but these some of the first applications I recommend installing whenever I (or a family member/friend) get a new system.

Top 10 open source Windows applications. (Lifehacker)