Remember: Rule #1 Always say "Yes" to donations. One of our participating schools just got a donation of cinder blocks. The coordinator was uncertain about how good they would be, esthetically pleasing? A quick search led to http://www.raised-bed-gardening.org/2009/04/building-cinder-block-raised-garden-bed.html
Not only are they good, they are inexpensive (really inexpensive if donated), and have many other positives. Check out the site. See link under our resources.