Worked at a non-profit for a while, and we had quite a few free licenses that were bought at the MS company store and then donated to us. They were a little tricky in their conditions, but nothing beats free for expensive licences.
For the record: http://techsoup.org is an organization that makes it easy for non-profits to get cheap/free software licenses and hardware. They've worked out deals with many major companies, not just Microsoft.
