Haven't been to any of these, but I did do the Renaissance Capital Beijing (the new one east 3rd ring road) about a month ago and they were running a 2 for 1 deal, for something that was already competitively priced. A very solid spread and fantastic service (one of my friends was vegetarian and the staff bent over backwards to help her out).

I think there are some other properties (IC Fin. Street?) that are also known for their brunches, but perhaps someone with more experience can be of help. Hopefully this is a start...