DIY garden stones - use a cake pan (from the thrift store)! Also, using clear contact paper to hold the mosaic pieces in place while the concrete sets is kind of brilliant. There is also a link to easy stepping stones using flagstone and grout
I think we Should do a craft day and Mass produce some of these Rubber Door Mats pressed into a concrete mold and later removed, to make stepping stones. There are lots of other smart concrete project ideas on this page.