In Beijing, the most popular hot pot is none other than Shua Yang Rou (刷羊肉), i.e., dipping slices of lamb into the hot pot. Typically, everyone gets his/her own small pot and tada, all you have to do is cook whatever you order. These are specialty stores which serve mostly lamb related items, like offals, etc... beef may be ordered as well but not the popular choice. However, you can still visit if you're vegetarian as there are lots of choices to choose from.
After the hot pot, you may also order skewered lamb (like those from Xinjiang) on the side. Yummy!
There is a very good hot pot restaurant near to the Forbidden City. If anyone needs the location, please email me. I was also told by a cab driver in Beijing that the city of Yangfan (enroute to the Great Wall) is famous for such hot pot. We did go and yes, it was excellent. However, that's a bit of travel as far as I'm concerned. But, if you're on the way, you must try!
Hot Pot is very popular in Beijing and Chongqing due to their cold weather. Outside China, it's extremely popular in South Korea too!