As Beijing is a "clean" city, a lot of hotels also will stop you or your "guest" from time to time, if you like to take your girl friend up to your room. The official regulation is, that no guest on the room (who are not registered) after 10:30 pm. So most time no problem, if you come before that time, but some hotels even will check, if your guest left in time (but only very less). So we start to collect a list with girl friendly hotels.
As we know, the following hotels should have no problem with girls in the room (at least when you arrive before 10:30 pm):
Tip: Most bigger Hotels also have a public area on other levels for restaurant, hotel, bar or coffee. If they check guest on the lobby levels, there is still a big chance for the girl to go up to the restaurant first, than use the elevator from here (most time here will be no security guard).
Tip: You should care a little bit for the outfit of the girl. If you stay in a high level hotel and the girl is dressed very "low level", the risk to get trouble will rise up a lot. So in worst case invest some RMB for a nice dress for her and rise up your chance for real fun later.
Updated June 2015
We would be very happy, if you also share and add your experience here, to extend our list and keep it up to date.