Personally it would be Red Dead Redemption and Jurassic Park, which I think would be pretty epic!

The result can either be a film or a video game.
Threesome: Pirates of the Caribbean (movie) + Port Royale (game) + The Elder Scrolls >> Game.
Alpha Centauri + American Psycho = .. wait, it already exists. It's Yang.
http://www.youtube.com/watch?v=U_hrYz_2uAk
Wong Kar-wai's In The Mood For Love and Pathologic...
That would just be far too depressing.
So Clockwork Orange + Dungeon Keeper....that would be unsettling.
Rambo with Stallone should come this year. As far I know its the first one. First Blood I believe.
Pirates of the Caribbean would be epic. I think too. Especially as MMORPG. Ive actually hoped that SOE would make modern version of Pirates of the Burning Sea sometimes, give little Pirates of the Caribbean twist to it and it would be fun.
The Lion King mixed with Psychonauts.
Imagine entering Scar's mind! It'd make the movie seem more awesome.
Lion King mixed with Daggerfall. Lion King mixed with Sly Cooper. Lion King mixed with Pokemon. Lion King mixed with Simcity. Lion King mixed with Doom.
Especially Lion King Doom and Lion King Psychonauts. Lion King Thief would just not be that fun. Lion King TES is already possible if you make the Khajiit look right.
Well... most http://i1205.photobucket.com/albums/bb428/secularsage/1Up%20Blog%20graphics/Spemin.jpg?t=1288183646
Fallout and Mad Max.
That would have some badass vehicle combat, personal choice, and huge maps, as well as being an RPG....
I think my brain just exploded.
Never going to happen, but Star Wars and TES style open world RPG.
Terranigma and...Serenity?
Actually if you replace Ark with River...that might work. Be a bit bizarre trying to mesh both worlds together though.(Maybe through River's unique view of the world)
Jacob's Ladder and Elder Scrolls. You are going to Hell, but at least you have a sword and a healing spell.