http://www.pcmag.com/article2/0,1759,2216,00.asp

It's hard to browse the Web or read a computer magazine without finding a reference to Linux, the operating-system wunderkind created by Linus Torvalds and developed by a host of others. But although Linux steals the headlines, ISPs and system administrators often choose one of the BSDs—a group of operating systems based on code polished during more than 20 years of research at one of America's leading academic institutions.

What are the BSDs? And why should you consider using them if you're looking for a non-Windows operating system?
Just browsing, found this.
It's a nicely written piece, that gives some details about the BSD options.
If you are thinking of investing time and effort into a different non-MS OS, or, if you are just curious as to what exactly BSD IS, then this is a good place to start.