I've got a few, one that I like is "Linux Administration: A Beginner's Guide" Osborne Press; Steve Shah. Only problem is it's a little outdated (it uses RedHat 6 as a base for explanation, and we're now at RedHat 8) but most of the explanations are pretty good (xinetd, sendmail, basic FTP/SSH/HTTP protocols, portmapper, getting around in the shell, NIC configuration, etc).
Alternatively you can get one of those Mac OS X Power Users books, which usually start off explaining the Aqua interface in ridiculous detail, and then get into the Darwin subsystem.
btoneill, is that the series that was mentioned in the movie 'Hackers' as "UNIX administrator's handbook, also known as the big ugly red book that won't fit on a shelf"? That thing was huge...