UPDATE:I've been told that this place has been torn down, MLK Library is no more.
Right now, I think this is the best place to skate in DC. It's located down on 10th and G. NW. There are more waxed ledges here of varying heights than you could ever need, which also allows lots of people to skate here without crashing into each other.
The spot is also completely hassle-free as far as I can tell. I've had cops walk by me many times while skating here, and I've never had a problem.
There's four ledges in a row on each side just like this one.
The one draw back to the place is just how ghetto it is. Unless you're with a group of people, this isn't a great place to be at night. I've seen people shooting up here, drugs deals going down, prostitutes being solicited, and all kinds of other things that city life has. Still, as a whole, people don't seem to bother skateboarders, just try to look mean or something I guess.
The library was the most featured spot in the DC Metrospective in 411 Video Magazine #27. It's a short skate away from Pulaski Park, making it the obvious place to go if you get kicked out of there.