i don't know if many people that pop in here really are much into newer tech rides, but the 450 moto-x singles adapted to a street platform, seems more and more viable as i scour the local craigslist adds. i found an article in short, explaining the ability to change one moto-x bike into four different racing contenders. obviously i am not a racer, nor will ever be one, but i wouldn't mind building a variation of each for street purposes.
450 supersingle article <----click
pretty slick if you ask me.