I acquired a free bookshelf from my boss a few years back and the thing is sturdy as heck. I have two ten gallons on top (it's like 48" long and only about 4 feet high) and I can put up to 3 All-Glass 2.5 gallon tanks on each shelf. I've even put screws under the shelves above the tanks to install strip lights to illuminate the tanks without having to put a light on each tank. I love it! I'll find a picture!
I've since started adding another row on the middle shelf since I had to clear out my breeding tank (I had two males living in there) So imagine the next shelf down being the same as the one with the two gallons!
This was an up close shot I took of it after I finished setting it up initially. I've changed it slightly since, but you get the idea...
So keep an eye out on craig'slist and local yard sales and usable trash sections at the dump and the like and find a gem like this! I got this completely free (save for the gas money I had to pay someone with a truck to get it to me, lol!) But you get the idea!
Be careful with some things from Ikea... while nice to look at, their stuff isn't the greatest quality if you want cheap. It is mostly made of particle board and can come apart easily if you don't put it together quite right... And you have to put EVERYTHING together yourself... lol and they only have pictures on the directions so they can use them in every country. It can be confusing! :/