Wombat on Grand Street btw. Leonard and Lorimer has lobster night every Tuesday. Lobster (no claws - boo) choice of 3 different preparations for $12. I have yet to try it myself, so I am not able to truly say if it is a deal or not.
i'll second centro vasco, though you have to get the lobster broiled, it's my favorite. as far as this being the 'best deal'...well that depends on how much lobster you eat. i usually do a 3 1/2 pounder that's around $60-70.