I would say any project that is non-trivial and is of some use. Does not have to be large. In fact it could even be of no practical use, if it shows some of you

I would say any project that is non-trivial and is of some use. Does not have to be large. In fact it could even be of no practical use, if it shows some of your programming skills and knowledge (preferably on aspects that also happen to be useful in jobs). But the projects with no practical use will likely have less chance of getting you what you want - though some chance still. As with many things, it depends - on the company / job / etc.