I have a Brother HL-5170DN laser printer.
Works very well and is network ready. I routinely print from Windows 2K, Windows XP, Mac OS 9, Mac OS X, and from my Newton 2100.
For printing envelopes it has a passthrough option. I usually just let the envelope go all the way through and skip the passthrough option. The envelopes are a little bit curled, but not bad at all. With the passthrough option the envelope comes out fine.