Have you asked your players what sort of game they'd like? I consider this an essential first step -- at the very least, you have to tell them what kind of game you'd like to run and see if the idea appeals to them.
Are you interested in running a game set largely in one area, with in-depth politics happening? Do you want to run a travel/exploration game, in which the characters encounter all sorts of spectacles? Will it be an epic campaign, in which the characters meet the Dark (or at least Grubby) Lord in the beginning and spend the whole game figuring out how to defeat him? Or will it be more episodic, with a series of smaller story arcs?
Do you want something light in tone? Grim? Mythic? Gritty? Are we talking Indiana Jones, or are we talking Dark Crystal? Or maybe it's historical in tone, a la Guy Gavriel Kay, or horrific, a la China Mieville?
I'd try to figure out these questions first, and then look for ideas that match the feel you're going for.
Daniel
Edit: awhile ago, the Rat Bastard forum held a Rat Bastard Iron DM tournament, in which the contestants created an entire campaign stretching from first level through epic levels. You could steal from it for campaign ideas; there's some funky stuff in there, including floating islands, trickster-priests, ancient squid gods, and more.
Here's the thread; it's long, but sometimes very juicy.