The 590DA1. The trigger pull was long and heavy, intended to resemble a DA revolver trigger.
http://www.mossberg.com/wp-content/u...5/04/590DA.pdf
Edit: Interesting -- it may actually BE a "double action" trigger. Page 6 of the manual(under Firing) says "Cycling the action chambers a round and partially cocks the hammer. Pulling the trigger fully rearward completes the cocking cycle and then dropss the hammer, firing the gun."