I spent some time searching the web for some cool texture animations and sky boxes.
Download Texture Animations
Each pack has more than 20 resources ready to be used with the game. You'll need to rename the files to .bmp in order to use them with RVGL but that's all.
Most resources have a sane license that's CC-BY at most. Many of them are CC0 which means you wouldn't even have to give any credit. I still recommend copying the specific resource's readme contents into your creation's readme, just to be sure.
The reason I started collecting texture animations is my Blender add-on, which now has features for creating texture animations with ease. It's all GUI based, so you don't have to deal with any Python scripts anymore.
Here are some lazily created preview pictures:
[HIDE=My favorite sky box][/HIDE]