You know those green or gray flower blocks you find at flower shops or the dollar store they work great, and will you are there they also sell many colours of sand you can use.
This is from Drew's lawout
"I use a bunch of different stuff for ground cover…A lot of it is natural…sifted dirt, ground up leaves, small twigs…I also use broken up bits of plaster that I paint to look like loose rock, & lately, I’ve started mixing wood ash with sifted dirt, & using that for ballast…I use bailing twine (jute) to make tall grass, & of coarse, there’s plenty of Woodland Scenics ground foam in there, too"
Pictures of his ground cover can be found at
http://www.the-gauge.com/showthread.php?t=21976
hope this helps don't forget about the flower dept at Walmarts also, or other craft stores.