Beer Mapping has come up a couple of times and I really like it as it's easy to pinpoint things with their Google Maps mashup.http://beermapping.com/city-beer-maps/
I don't have as much faith in Beerfly reviews on BeerAdvocate. I've seen places I really enjoyed dissed pretty hard but it is useful for putting a list together for further research. You also have to be registered to use its fancier features. But here's a tip: Enter this into Google to get a quick list:
city name beerfly site:beeradvocate.com
Fancy a Pint is a great UK based site. It's London centric, though. I used this on my last trip and found a great local pub that I would have otherwise missed.http://www.fancyapint.com/
Beer in the Evening is another English site. It has broader coverage than Fancy a Pint. It also has a pub crawl generator, which is fun to play around with.http://www.beerintheevening.com/
Now post your favorites.