Buy a proper stand! Most LFS will sell you one seperate - doesnt matter if its a little bigger - but trust me dont try to use book cases or cheaply made furniture - i've seen the after affects!
I got my current stand at my lfs, but i got a different one off ebay that was rubbish! If you are thinkking of buying one off ebay contact the seller and ask if you can see it before bidding.
If that doesn't appeal to you, you can always purchase a stand. Just be sure that it is the proper size for your tank! Also remember that a filled aquarium weighs approximately 10 Lbs per gallon....so a 30 gallon tank weighs ~300 lbs!