Hi visitor !
I'm not writing this post because NetBSD 6.0 is out, I should but I don't want to say the same thing as all the others blogs.
I'm writing about the state of the Raspberry PI on NetBSD. You should have seen in the 6.0 release notes that there is a support for it. YES, it may boot your PI, but you can only get a serial connection to your device and type some commands. Tere is a lot more work to do, but this seems promising !
Please find this thread from netbsd mailing list port-arm, there is a link to download a bootable image of netbsd for raspberry pi !
If you are interested about FreeBSD on raspberry pi you should follow this blog made by someone who wants to port FreeBSD to the PI. He made U-boot boot on the PI and boot FreeBSD, but the support seems a bit behind NetBSD.
For OpenBSD, no port planned. And DragonFly doesn't exist on ARM.
Extra : I know this is not BSD, but you can run RISC OS on the Raspberry PI (I tried and it works wonderfully !) The forum thread is here