Check this out:
Its a free dance mat game for PC, Linux, and Mac.
You can use a dance mat, or just simply a keyboard (Like I'm using at the moment).
It has different packs to download, and themes, backgrounds, etc.
You can find loads of packs if you know where to look
Loads of songs are on that site also.
Its brilliant, and simulates DDR, and the new one with diagnal arrows
You'll be a pro soon if you keep working at the songs like I am
I can do all of them so far on Medium.