Eggcrate is cheap and easy to make your own with some zip ties but doesn't look as nice until it gets coated with coraline. A 4'x2' is readily available at hardware store for $13 in white, black can be found but can run you about twice as much, I found some through a company called frontierlighting (Part# 8161) and Eplastics.com but they have to order online and pay for shipping for a 4'x2' piece.
The Eshopps frag racks are pretty cool but the magnets are weak, I use the sure grip 50 magnet sandwhiched in between the rack lip and the glass, be carefull with this magnet though, it's super powerfull, don't think it can crush bone but can leave a stingy bruise.
Once I set up my frag tank I may have my eshopps rack for sale but I think I'm just going to keep it, everyone loves frags and I keep running out of room for frags.