DIY natural swimming pool - the video provided in the link is pretty cool. I've had dreams of these things, and now that I've seen an actual video I'm a bit kreeped out because I don't like swimming in dark water, but the pool itself is pretty awesome
DIY - Homemade Gabion wall ie rocks encased in wire baskets and used as a retaining wall - creates a dramatic feature in a garden. No directions on link. Nice someone figured out how to landscape with river rock. I swear they grow!