I went to Jo Burger in Rathmines this weekend, it's already been blogged about here and there and its somewhat crumpleresque website has been commented on here. For those of you who lack patience, you scroll right!
Gourmet burgers are becoming quite the thing, Real* Gourmet Burger on the pavilion in Dun Laoghaire offers a "nutritious and sophisticated" organic burger menu that's not awful, if you are willing to endure the wait for a table (it's very popular) and the surly front of house (not so popular)
Jo Burger is a decidedly more friendly place, the menus are wrapped up in a variety of old annuals (I got a Beano one) and there is a fairly mind boggling selection of burger options available, I had The Dobson - basically a cheeseburger - delicous.
The walls have graffiti style murals, retro lampshades hang from the ceiling and a DJ is in the house 'til 2am Friday and Saturday night. It's all very New York in the Nineties, I believe it gets very busy, but if you get a chance to try it, do.