Planescape is a good option.
I'm often a victim of this as a player, and it can happen as a DM too.
If you're feeling uncreative with your current campaign, talk it up with your players, maybe you can put it on hold and take up the mantle of a player for a bit, or run a one-shot.
Additionally, sometimes it can really help to read a bunch of different sources. Then just jot down all your spontaneous ideas and then walk away from them for a couple days. Go back, look at them, scratch out the ones that you don't understand or think are silly, whatnot, and focus on the ones that while might have been random could become very interesting threads to work with.
Also, on a rules standpoint, I find it very easy to bounce from one cool thing to the next, but I find if I make the character/personality/setting/feel first and really put myself into it, then I find when it comes to the crunchy rules bits, I'm a lot less flaky and can hold to the original concept alot better.