I you're looking for ready to run adventures, not just a setting, then I'd take a look at Shadow World or Echoes of Heaven, the authors of both are around here (Terry Amthor and Robert Defendi).
I second that as well.
1) Shadow World has great "companions" if you want to look at them in that sense. While they are part of a larger world system, the individual books are great add-ins to an existing world, or in your case, a great jumping off point.
I picked up Quellbourne many years ago to see what a "pre-made world" for RM looked like. I knew D&D had their own pre-made worlds and all the adventures took place inside that world and it was one of the reasons I am put off by that system. I started to looked at the Companion and I fell in love with the world, at the very least, I fell in love with that little portion of the world. Now that I've started GM-ing again for newbies and for my own family, I've started looking into getting more of those modules. I can use them as stand alone adventures, or I can incorporate them as permanent locales within my own world. You can easily run a 4-5 quests out of Quellbourne alone.
2) When I first started GM-ing back in college, I asked one of our most creative GM's how he did it. How did he come up with all of these amazing adventures and ideas? He said "It's simple. Create an adventure that YOU want to be in; a world that would be fun to you, then it goes from there. If YOU or your character want to be there, and it's interesting to you, then you start having fun. Once you are having fun as the GM, everyone else gets into it and starts to have fun."
Once you are having fun in your own little world, it's easier and to deal with questions as they pop up. Once you start having a blast with your creation, the players feed off that excitement and they help your world develop.
