Home Depot gift card, Kitchen appliances, pretty much any item around the house you can think of.
Though it depends, if they're moving from their parents' or if they're just moving from another place that they owned/rented. If they're not moving from their parents' than they'll have everything already so just stick with a gift card.
Weed scented furnace filters are also a great gift, it's a gift that keeps on giving. Wait, I said that as a joke, but I think that actually is an awesome idea. I need to patent that.