Okay, I have a little bit of information to give, as my dear significant other has been asking for this thing for 16 months, it's a great weight loss tool by the way!
Nonetheless, from every thing that I have read, do not purchase a soft pad, because they all suck, when I say they all suck, I mean some of them do not allow you to wear shoes while playing them, some slide around on the floor, other's stop working after a week, maybe 2 months.
Your best bet is to get a metal pad. Do not purchase any metal pads with the number TX in front of them (these are widely sold on e-bay). There is the redoctane after burner, this works on ps2, x-box, game cube, and the best one on the market which is a colbalt flux. The Colbalt flux is currently only available on PS2 however they are working on getting an xbox version (we have 2 x-boxes). If you have a ps2 go for the colbalt, it's a large investment but it's the best pad on the market and it last! In addition to that, there are more games available on the PS2, not only can you get DDR games (Dance Dance Revolution 1-3) The 3rd one is actually being released on the 15th of this month, but you can also get In the Groove, which I've heard is much better than Dance Dance Revolution games.
Toys R us, amazon.com and
walmart all have the DDR games, the 1st edition is $19.99 and the 2nd is $34.95 and the 3rd one is on pre-order for $38 (I ordered them just the other day)
Now to the bad news....
The colbalt flux is $299 plus $50 shipping and handling
The Red Octane afterburner is $199 plus $50 shipping and handling
The Red Octane ignition (I think that's what it is called, is the best soft/hard sturdy reliable pad on the market) it is $99 and is available at gamestop.com
If you want more DDR information go to www (dot) ddrfreaks (dot) com