The following picture from APOD is one of the cooler ones they've had for a while. It talks about fermions and why matter doesn't collapse upon itself. It seems that while bosons can contract and occupy the same space as the temperature drops, fermions can only exist one to a quantum energy state. At least that's one spin on it.
Read the article, it explains it much better than I can. One of the better links to follow from that page is the one at The Particle Adventure.