I'm currently developing a demo for the latest features of the game engine. For me, the hardest part of developing a game demo is not the programming part, but the artistic aspect. I spend days looking for game characters and game environment ideas. Moreover, since I am not an artist and I'm the only one working on this, I look for ideas which I can create.
You may be an indie-game developer who plays the role of the programmer and the artist. And you may have the same problem as I do.
If that is the case, the next time you are looking for ideas, search for them on Pinterest. For example, I did a search for "low poly models" and these were some of the ideas that caught my attention:
This site has given me plenty of game ideas. You may want to give it a shot the next time you are out of ideas.