Megabus is now offering service in the US and is currently running a deal exactly like National Express' funfares. These fares are only $1.00 between Midwest cities Chicago, Minneapolis/St. Paul, St. Louis, Milwaulkee, Detroit, Cleveland, Indianapolis, Columbus, and Cincinnati.
Megabus' US site
This should hopefully be helpful to both domestic T-Punks and visitors from overseas looking for a cheap option to travel between some cities without risking the shadyness of Greyhound.