I’ll leave the ones up for now, but the long and the short of it is, thanks to the short-sightedness and greed of the State of Colorado, Amazon has closed all Associates accounts within Colorado.
OK, so the calendar I checked from Wizards only listed Underdark, but apparently there’s a second book out this month: Player’s Handbook Races: Dragonborn
Underdark™ contains everything a Dungeon Master needs to run adventures or campaigns set in the vast underworld of his or her D&D campaign, including new monsters and hazards, ready-to-play encounters, monster lairs, and detailed information on various dark-dwelling “movers and shakers.”