Hot on the heels of EWs first look at Final Crisis, Wizard has just posted a preview of the Final Crisis special Legion of Three Worlds. As you can see by page 5 this event is being choreographed by Geoff Johns and George Perez (and that we're going to have to wait till August to read it, do'h). Legion of Three worlds is a team-up of three different Legion Teams in order to stop Superman(boy) Prime. The teams are actually the original Legion from Johns' Superman time-travelling story, the "Zero Hour" era Legion, and the Mark Waid-Barry Kitson "teen" Legion (present incarnation). According to Johns' this event is similar to what Green Lantern: Rebirth was for the Green Lanterns (housecleaning, updating, re-imagining).
For those at a loss, pick up the recent Action Comics run, as it serves as a lead-in for "Three Worlds". Pay particular attention to the Time Trapper and the Legion of Super-Villains, he's a central villain to the Three Worlds Event and Superman(boy) Prime leads the twisted incarnation of the Legion (evil mash-up). Too bad we have to wait to see it. Maybe this will help tide us over till Blackest Night.
Enjoy the preview in the meantime!