I can't speak for FreeBSD, but for OpenBSD at least, I've had decent experiences with my Dell Latitude D830. Good hardware support, though networking and power management were a little iffy (the Intel wireless required a firmware download, and it was really touchy about hibernation, though that might have been a configuration issue on my part, seeing as this was the first of many OpenBSD installs I've done).

I've since been using it for other OS experiments (Haiku for awhile; now I'm venturing into MINIX), but it handled OpenBSD (and Slackware before it) rather nicely, and I don't imagine FreeBSD would be any worse.

Now, that's not modern at all, but I'm willing to bet that a more modern enterprise-like Dell would be similar in build but with newer components.