Lots of open source projects raise money from their user communities by soliciting donations. Most open source projects will have the 'Support' or 'Make a Donation' button on their home page or download page. At Eclipse we have had the Friend of Eclipse program for a number of years to solicit financial support for our community.
Earlier this year, we started looking for ways to increase the number of users making donations.
"I wanted to share these results with everyone so other open source projects might be able to learn from our experience. It was a relatively simple change. Ask for a donation when the download is occurring not when a user is browsing the project site."