I disagree with sml that OpenBSD is not for newbies. I have used several distros of Linux and I did not like most of them. Slackware was the one that taught me the most. Debian is also a great distro for any hardware (those are the only 2 distros I will use now if I have the choice). But OpenBSD *REALLY* got me interrested in UNIX. Its clean, the documentation is great, and the stability is worth the $40 for the cds. I recommend OpenBSD for anyone that wants to learn the ins and out of a UNIX-like OS. Plus, make build is wonderful for optimizing the code for the hardware you are on. 🙂
FreeBSD is also a good choice, but Ive had problems with every release Ive used. OpenBSD just seemed to be cleaner. But these are just my opinions of course 🙂