As for motorcycle tires. Avon is coming out with the Cobra tires in our sizes as we speak. Also.. the new Suzuki C109RT has a 240/55-16 rear tire, but I'm not sure who makes it yet. So we'll have three choices of motorcycle tires real soon.
Of course, if you go to the dark side, like Greg said, your options are much greater. I think I'll be sticking with motorcycle tires for now. I'm hoping the Avons will be readily real soon as both of my tires will be needing replacement in the next month or so.