I used cinder blocks for years before I finally bought stands.
It was nice because I had five tanks at the time, a 20, a 29, a 40 show, and two ten gallon tanks. I lined three tanks along one wall, and two along the other and had the tanks meet at the corner. I used different amounts of blocks so that they weren't all the same height. You could sit there for hours and never get bored. I sort of miss it now.
