I think you want more than a lot of data. That's a good start, but you also want it to be structured in a way that requires some thought (or just in 3+ normal

I think you want more than a lot of data. That's a good start, but you also want it to be structured in a way that requires some thought (or just in 3+ normal form). Have someone ask for a report out of it (or come up with as many reports as you can). I wish I had a suggestion for such a data set. Microsoft's famous case is Northwind, but I don't know where you might find it (without having searched just now).