At most any hardware store, you can buy a variety of stick-on rubber feet. They may be round, square, whatever.They are usually about 1/4" thick, or so. You can stick two or three of them, stacked, on the existing feet of your equipment, providing 3/4 - 1" spacing between DVD players, DVDRs and VCRs. Those pieces of equipment don't produce much heat. For AVRs, amps, older Moto DVRs, you need at least a couple of inches, better three or more. And, of course heavy equipment should never be stacked on light equipment.
I have an equipment stack 6' tall, w/o amps or speakers. Almost everything is on separate shelves in my equip. rack, with plenty of space. But, using my spacer method above, I have one stack of two DVDRs, and a DVD player on one shelf, and another stack of a 400 disc DVD changer, with two SVHS VCRs on top on another shelf. I have never had any problems, even though I don't have air conditioning (just fans), and it gets hot in the house in the summer.
Oh, there are a ZILLION varieties of equipment racks, designed to allow plenty of breathing space between components. Good ones ain't cheap!