I agree with Bill. It's a huge pain to have tanks very close to the floor (and even a bigger pain to have them too high). I had a stand that held 2 20-gallon tanks stacked one on top of the other, but eventually got disgusted with it because the bottom tank was such a pain to maintenance and also difficult for me to enjoy unless sitting or laying in an uncomfortable position.
Although that's totally up to you. If they're experimental or breeding tanks, then you may purposely want them out of the way, which I can certainly understand.
I just recently made a stand for 2 tanks out of a modified (read: heavily reinforced) entertainment center. It holds 2 20-gallons side by side. It's lower to the ground than I'd like, but when sitting in my recliner, the tank is at eye level, which suits me perfectly fine. I'll take pictures sometime.