I just read Predator Vs. Judge Dredd. That's a combination that kicks arse, right? Surprisingly, not really. Maybe the writing was a bit pedestrian, and the whole thing a bit rushed, but it might be because Judge Dredd is such a crazed Crapsack World
of mutants, war-bots, Dark Judges, nuclear war and what-the-hell-else that, though the Predator is a serious badass, an invisible alien game-hunter on a Judge-killing trail of manhood is almost par for the course.
X-Files meets Stargate or Early Edition both sound good.
Though somewhat obvious, this could be awesome (and cause raging fanboy madness): a Star Destroyer drifts into Earth space. They don't know how they got there. Starts with Department of Defence agents picking up America's second-biggest authority on Star Wars gear ("We tried another guy. He was uncooperative." "Oh, yeah. He's a dick.") The money shots for the trailer: "That's not a asteroid." TIE Fighters vs the Air Force! AT-A Ts
march on major cities (choppers try to wind up their legs!) Stormtroopers are actually pretty hard! The Star Destroyer crashes into the Moon!
Could be great. Could suck. Curiously, I'm not a Star Wars fanboy.