I disagree with others that say who cares if a new one is around the corner. But in this case it doesn't matter because iPad 3 will not be coming out this fall or winter. I say this because repeated rumors indicate all the major new components presumed to be in the new iPad are not ready for production. If you do your research and see how long it takes for Apple's new products to go from production to release, you will see that it is impossible to have a fall iPad update.
OP, I would buy the iPad 2 now, unless you are okay waiting until April 2012. Rumors and previous Apple behavior points to this as the most likely date.
Also bare in mind that iPads hold their value quite well. When the iPad 2 came out there were quite a few people selling for cheap since the market was flooded, but about a month after release the used iPad 1 prices rose.