DDR is Wii-bound, and if you're going to REALLY get into the game, consider a
Cobalt Flux.
I own one and it's easily the best pad in the industry. It's lasted for roughly two years now and I haven't even cleaned it. Soft pads will die in a matter of a month with regular use and at $25 a pop, you're better off shelling out the $300 and getting a pad which will last AND allow you to improve all the way up to 10 footers, if necessary.
The one downside is that they don't yet have the
control box to connect it to a GC port yet. I've emailed them about it, as well as included a link to the article about DDR coming to the Wii, asking if they intend to make one. If other people want to pester them about it, that would be great. Maybe we could get them to build a GC version next.
There's a plethora of varying pads to be found
here, but speaking as a guy who has tried other hard pad brands in the past, save yourself the time and go for a CFlux.