I think I like the way Tom summed it up the best - that you just want the new person to be comfortable and feel at home. I always like to make sure people know what's expected of them, too. There's nothing worse than going into a job and not knowing what you're supposed to accomplish, and what the priorities are. This happens more often than it should.
All that basic info that other people mentioned is really great. But the most valuable part of orientation is to make the new person want to be there and want to do their best. Piss them off on the first day, and their desire to do their best for you is diminished.