These are the simulators and where to get them.
StepMania
www.stepmania.com
StepMania Online
www.stepmaniaonline.com
Dance With Intensity
http://dwi.ddruk.com
Delight Delight Reduplication
http://homepage1.nifty.com/nickle/
Diet Diet Revolution (DDR99)
http://www.akddr.com/ddrdownload.shtml
Flash Flash Revolution
http://www.flashflashrevolution.com/
pydance
http://www.icculus.org/pyddr/
This list will expand.