What's nice about drawing in public settings (besides the obvious thrill of working from live, unknowing models) is that your usual concerns about art-making are reversed. You want to use fewer materials, not more; you want bad lighting, not good, so as to not call attention to yourself. Of course, no matter how dark it is you're going to have to contend with people looking over your shoulder wondering what the hell you're doing--and as such, you need to make sure to draw in a place where either a) no one will talk to you or b) the people who talk to you will be interesting and good-natured. A guide to my preferred hotspots below: The Gibson: One of my favorite places to draw, although pricey--poorly lit, strong cocktails, friendly barstaff, and generally an intriguing crowd. Also, a good place to go to after visiting the surrounding galleries in the area and you're feeling inspired (or bitter, depending on what's on exhibit).
Busboys and Poets: Ideal for when you want to be surrounded by fellow artsy people, but don't necessarily want to be bothered by them. Also would recommend Open City Diner or Tryst if you're in a chattier mood and hankering similar coffee shop fare.
Vinoteca: Are you depressed? Do you need to drink away your problems? But draw while doing so? This is the place to go.
Oya: You will look funny drawing here. But who cares, no? Recommended on weeknights when you can catch the happy hour specials.
Elephant and Castle: Being an English style restaurant, I thought this would be one of the better spots in the city--I have happy memories of scribbling away in Oxford's cozy pubs--but the only time I attempted to draw here, I found myself sitting next to an angry Irish guy ranting bitterly about American politics and I had no choice but to nod politely for twenty minutes. Probably worth a second shot, though.