DonorsChoose.org
I recently learned about a new initiative from DonorsChoose.org, a non-profit that accepts grant requests from K-12 teachers and makes them available to donors from across the country. DonorsChoose has set up BloggersChoose.org, a way for us bloggers to spread the word. Anyone can create a challenge, and then publicize it.
I've set up one on Economics and the World, though the only proposal I've found to include so far is one that's local: a high school in Richmond, CA. I've set a rather ambitious goal of $800, especially since this blog has been dormant for nearly a year.
If you're not in a position to give, consider putting together your own challenge, and publicizing it to your network!