Since finding whole packs of step files can be difficult, I will periodically update this blog with a few entries of both new and old packs that I come in contact with. One of my links on my other blog has a large list of packs you can sort through and download.
I figure looking at all those packs might be a bit much to sort through at all at once, so I will post one of my personal favorites:
This is one of the more well known stepmania song packs created, aside from the Tournamix Series. Keyboard Collab sports some fun charts for all skill levels, and maybe a few things you could modify and put on your USB to try on an ITG R21 cabinet. [For advanced players]
If you are looking for something that you can play at home that resembles DDR songs, this should be fun and useful for you:
Spork! DDR Encore
Here are a few examples of songs you will find there [click to download]:
There are literally dozens of songs listed on Spork's site that feature songs that you can play that are similar in difficulty to Dance Dance Revolution songs. Difficulties range from 1-10, just like the songs for DDR. If you have a pad at home and Stepmania, you can give them a run for yourself!