@zjv5002,

The Great Wall is absolutely worth seeing. Tiananmen Square and the Forbidden City both feel somewhat oppressive, but the Beihai and Gulou districts to the north still have a hutong feel and are nice just to walk around. The Soong Qingling residence (on the northern part of Houhai) is worth visiting, and - further away from the center of town - the 798 art district in Chaoyang is worth a walk. Beijing and Tsinghua Universities are in the other direction and have beautiful campuses. The Summer Palace is not too far from there and also a must see.

One of the nicest times to see the downtown area around the Forbidden City for my money is actually in the late evening. They close the entrance to the palace museum itself, but the park is still open and walkable, and it's nicer since it's cooler and often very empty.

For Mongolian stuff, you can check with Alc at Amilal -- he runs the place and has bands in on occasion. Feel free to mention David and Brendan sent you and maybe we'll get a free drink out of it. :) Address here: [http://www.thebeijinger.com/directory/Amilal]