I agree: make sure it has postscript and built-in networking.
I've been completely satisfied with my HP LaserJet 6MP for many years. I'm starting to look for a new printer, now, though, because Apple has finally dropped support for AppleTalk in Snow Leopard! So while the printer still works fine, I can no longer print to it from my main Macs. I have an always-on Linux server, so I used CUPS to set it up as a shared printer, and am able to print through the Linux box, for now. It's not ideal, though, since printing via CUPS gets me an extra page with a postscript error after every print job.