There are tons of great restaurants in Beijing! One of my favourites is a Japanese place in Sanlitun area. It's a bit more expensive, but it's worth every RMB. Expect to spend around 150 RMB for a nice dinner.
4 Gongti Bei Lu, Sanlitun
Opposite Rock and Roll Club
If you want to go Chinese, I suggest going to "The Yunnan Restaurant".. It doesn't really have a name, but food is delicious and it's cheap. Find it on the opposite of Le little Saigon.
Le little Saigon