As of right now, there are four DDR games released in the US for DDR. These are DDR:MAX, DDR:MAX2, DDR:EXTREME, and DDR:EXTREME2. I own Max, Max2, and Extreme. They're all ok, while I prefer Max to Extreme. I'm using a RedOctane Ignition 3.0 (Soft Pad) and I couldn't be happier. Another plus of this pad (which means maybe RedOctane does it with their metal pads) is that it has a USB hookup, so you can hook it up to your computer, and using a program called StepMania, you can play DDR on your computer, without being confined to a single disc worth of songs. (I think I've got 700+ songs right now.)

EDIT: The RedOctane metal pad (Afterburner) DOES have USB support, but it runs $250 USD.