Valve have released their update treatment for the Scout class today. It features 3 new unlockable weapons, achievements, and a range of new maps and map updates. And a smaller mini-HUD, apparently. Get the skinny here: http://www.teamfortress.com/scoutupdate/

Rumor has it the Spy will be next in line for an update. A major L4D update is expected in late March to May, featuring 2 new versus maps.