Some thoughts. I didn't really start the thread with anything specific in mind, but off the top of my head...
Malazan Book of the Fallen. I don't know if it would translate all that well, without a clear central cast of characters (or rather, several changing ones). But the ideas and world are great - it is big, fat fantasy with pizazz and its own unique vibe. Probably not my first choice, though - I'd rather see it as an RPG.
CJ Cherryh's Book of Morgaine. Sort of on the fringe between classic and cult classic science fantasy. World-hopping with slow-burn romance would make for a great series - and could be extended beyond what Cherryh wrote, with infinite possibilities.
Dragonlance Chronicles. With good actors and better-than-Weis/Hickman screenwriters. It is probably the single D&D story that would translate best to a big epic fantasy trilogy (or series). It always felt a bit like a potentially great work written by two people with good ideas but poor writing skills.
Silver Surfer. I know, we've seen him on screen and are going to see her again. But a series centered on the Surfer in space would be (or could be) grand.
A new science fiction epic. Not sure what, but I'm ready to move on from Star Wars/Trek. Not sure what the right choice would be, but would love to see something with a bit of the optimism of Wars/Trek, but not whitewashing the darkness.