If the Mac Mini’s 5 USB ports are still somehow not enough for your needs (and you don’t have one of these), then get one of these bad boys.
As you can see, you can connect this multi-ported monstrosity to 2 computers, but they can only access the hub one at a time. Since it’s so huge, it’s understandable that it needs to be plugged to work. You can order one (it’s a 16-in-1, really) at Geek Stuff 4 U for $105 USD. I heard that if you daisy chain these beasts, the explosion that ensues will create anti-matter.