BSD and FreeBSD are not Linux distributions, they are an actual genre of Unix OS all in themselves
linux distributions are the same OS different kernels, and packages, to name a few of good ones I know of (the top two being equally my favorite)
Mandrake 7.2
Suse Linux 7.0 Professional
RedHat 6.*
Debian Linux
Turbo Linux
and many many more.
The different distributions have different things, like either the latest Kernel (the core of linux) , different styles of instalations, different packages, Xwindows, etc.
it's sort of like this, imagine if windows were opensource, and very configuratble, you would see several versions of windows, it looks like windows and such, but set up different, comming with lots of different software bundles and games and such.
so basically when you see a distribution, it's just packaged differently. Karl Blessing aka kb244{fastHACK}