So far, I've just found this guide to London pubs. However, it is so complete that I doubt you would ever need another. Each pub (there are hundreds listed!) has ratings for everything from beer, measures, prices, to music, food and toilets.
If you want a more specific guide, check out this one for Covent Garden, which includes a pub guide.
Clem's Pub Crawl Pages. These are quite cool - there are 19 accounts of pub crawls around London, including the famed Monopoly Pub Crawl. The detail is excellent, with beer types, prices, directions, bus numbers and sometimes even the character of the bar staff!
Another Monopoly Pub Crawl with good directions and a well thought out route.