Gold Mountain is probably one of the better restaurants for dim sum in San Francisco Chinatown. They serve up good versions all of the types of dim sum and the food isn't horribly greasy like at other places. There is also a nice variety of menu items such as fried noodles, fried rice, and veggies. The waitstaff is good about circulating various items in carts, though the earlier you go, the better.
Be prepared to fight for a table on weekend mornings as the restaurant will be packed.