Not sure if you are just looking for a good idea for a collab, or a specific theme or not, but I had a pretty sweet idea. Although I would suck at putting together a collab, I think this idea would turn out well if we got enough people.
The Walk Cycle Collab!
So I was figuring it could work out in two ways, either each person does an entire walk cycle for a character similar to the proportions in the pic I am posting with this, OR each part of the walk cycle is done by a different person, so you can have the character changing with every movement! Then there can be a number of people doing each step, so it adds up to a long crazy changing animation! We can think of a funny background to put the characters in afterwards, keeping the background blank and adding it in flash later on. Let me know what you guys think!
searched for it in the search bar, nothing came up, so I hope it hasn't been done before :p