Black Iron Burger on East 5th between A & B. Get the special. And they've got good beers on tap. Nothing like BIB. The incredibly hot grill and the amazing beef. Try it, you'll be a convert.
Other good spots in the nabe include East Village Tavern (under-rated sliders and Cask Ale) and the too-popular Royale.
Ahhhhhhh, Pipers Kilt. I used to love going there. Their burgers were good, but their All You Can Drink Sunday Brunch was the best. The best burger I had was at a bar called McCales or McAles, on 9th ave in the mid 40's, west of the Marriot. We used to call them brontosaurus-burgers because it was the size of the plate. That with a side of steak fries (and some lipator) made for a great lunch. It was also the place that they filmed the bar scenes in the movie Money Train.......
Anyway that bar is gone now and I haven't been to Pipers Kilt in 15 years.
Sunday brunch @ pipers is the BEST!! All you drink and breakfast or any burger great times.
My 2 best burgers were at a bar called the "Dakota RoadHouse" it's located between Church Street and West Broadway 3-4 blocks North of 7WTC, I guess the best way to find it NOWADAYS is to go to the controversal proposed mosque site and it's just to the left of it - not the kind of notoriety they were looking for. Also, Jackson Hole has amazing burgers whichever one you go to (there are several locations), there is one on 2nd Ave in the 70"s??