A friend of mine who lives in Beijing has set up a website categorising all the Bars in Beijing.
It's still a work in progress, but he has listed over 500 bars so far. For a place as big as Beijing, you can imagine that there's going to be a lot of bars. They're categorised by location, and if they are a night club, a bar, or a KTV(karaoke) place etc.
He still wants to add photos for all of the bars, and just generally make it a nice guide to Beijing bars.