A slightly improved version of the iPad 2 could also be released around that time, to be sold alongside the current version. September's Apple event could be a lot more than just new iPods.
iPad 2 only just launched yesterday in various other countries. It will most likely sell out there this weekend as well. Most people still have a few weeks to wait for ordered iPad 2's. They can barely meet demand now. App developers have barely even scratched the surface of updating and writing apps to take advantage of all the new goodies in the iPad 2. With the tragedy in Japan, some components are in short supply. iPad 2 has barely gotten out of the gate! With a track record like that for the iPad 2, I just can't see how anyone can believe any type of iPad 3 launch will take place in the Fall. Besides, that's when they launch iPods for Xmas anyway. They already have a product schedule for that window. "2011 is the Year of iPad 2".
Look for iPad 3 March/April 2012.