Miaghstir: You're saying there's supposed to be another three movies sometime in the future?
I'm pretty sure Lucas said in some interview that the main story is just Anakin's/Vader's rise, tragic fall, and final redemption - which is fully told now.
Originally there were scripts for three trilogies. All pretty loose, but enough to plot key events that happen in each. And, like I said, he went with the middle one first.
The ones that come after include Skywalker's attempts to rebuild the Jedi order which is alluded to in some Star Wars games. But it was stated by Lucas that he would not be developing that trilogy as films. But then the same was said of 1-3.