Safari, jungle, or focus on a color scheme (at least 3 main colors with at least 2 accent colors) and a specific creature, nautical or under the sea (for mine, I'm thinking of under the sea). Then there's always characters or objects you can focus on (I.e. pooh bear/trains). OH! And I love the theme of "once upon a time" (fairy tale book theme). Or you could just do theme colors and focus on textures (polka dots, stripes, chevron stripes, florals, etc.).
Pinterest is a great resource; tons of great ideas. Download the app it's free.