Creating a collaborative project for a group of 10 graduate neuroscience students from various backgrounds
Sometimes the hardest part is figuring out what the project should be. 

I use a large-group project for one of my classes, and I've started soliciting faculty in certain departments with an email a few months before class gets underway.  Essentially, this email states:


My class will be working on a semester-long project soon.
I would rather the students work on something real-world, as opposed to a toy project.
Because these are students, there are no guarantees you'll get a useful result when they are done. However, you won't pay anything, either, and you might get lucky.
If you have something that might be a suitable idea, contact me.


The result has been a big success. Students tend to work harder when they feel like something useful and tangible may come from their efforts. Moreover, this set-up requires the students to work with real "customers", which is sometimes one of the most valuable parts of the learning process.