I got a Brother 8860-DN at Costco. It prints, scans, copies, and does duplexing. It's got a built-in network interface, and just plain works. It was trivial to set it up to print from any machine on our network. For $350 or so, it can't be beat! Consumables are not very expensive, either.
Edited to add: Brother has drivers for all sorts of operating systems. I was pleasantly surprised by their support of Windows XP x64