I originally wrote this as a comment on a discussion forum, but decided to post here as well so I can easily refer people to it. This was written September 2012.
Bars/pubs I can personally vouch for:
Craft Beer Company - Beer nerd bar, lots on tap and on cask. Recommend you go early afternoon, can get slammed in the evening.
Cask Pub & Kitchen - Sister pub of Craft Beer Co. A bit smaller draft/cask selection, but usually less crowded.
The Jolly Butchers - North London (N16). My local. A bit out of the way but worth a stop if you’re in the area.
The Rake - Really small bar but good beer on tap, big bottle selection. They also run a stall in Borough Market called Utobeer which is probably one of the best “bottle shops” in London.
BrewDog Shoreditch - This used to be Mason & Taylors. Decent selection of bottles, quite a bit of American bottled bers. Lots of BrewDog beers on tap if you’re into that. Highlight for me is their selection of guest taps, which often includes the likes of Mikkeller, Firestone Walker, Rogue, etc. Note that there are no cask beers here. Most staff are knowledgeable, all are more than willing to help you out. Ask for samples!
The Royal Oak - This is not a craft beer place, but go here for an old-school victorian-era English pub experience. Order anything by Harvey’s Brewery, relax and enjoy.
Bars I haven’t been to yet, but are good:
BrewDog Camden - Supposedly a bit more expensive, but good selection of BrewDog beers and others on tap.
Euston Tap - Right outside Euston station, small bar with big selection. Unique setting as it’s in an old gatehouse.
Southampton Arms - Very good spot for UK-only beers, as that’s all they sell. A longstanding staple in the London craft beer scene. Heard good things.
Drink anything by these breweries:
Kernel - Some of the best beer in London in my opinion. Fantastic American IPA, Evin knows his hops. Their porters and stouts are very straightforward and delicious as well, low on the bullshit and big on flavour. Go to their brewery on a Saturday before 3PM to buy beer direct and hang out and drink on site. They’ll usually give you a tour as well if you ask.
Brodies - Hackney Red is great. Dalston Black IPA is outstanding. They’ve done a collab w/ Mikkeller and some crazy stuff like a White IPA, Coffee IPA, Brett IPA, a sour or two.
Camden Town - These guys move a lot of product and have really good distribution throughout London. Their Camden Lager is everywhere. Their beers you see in pubs are a bit tame, but decent. I drink them over Stella/Kronenbourg/Carlsberg any day. They’re starting to branch out and do more creative stuff, but it’s small batch and you may have to go to their brewery bar to get it. Their brewery is a cool place to hang out and drink though, I definitely recommend checking it out.
Redemption - Big Chief, a cask American IPA, holds a special place in my heart. Trinity is a great 3.0% session beer too.
Dark Star - Hophead is a pretty common and sessionable pale ale. American Pale Ale is really good. Revelation is one of my favourite London beers, really really great.
Thornbridge - Martin Dickie brewed for Thornbridge before leaving to cofound BrewDog. Their Jaipur IPA is great.
Magic Rock - Good nicely hopped beers. High Wire pale ale, Cannonball IPA, and Surreal Stout are some you should look out for.
Hardknott - Mostly good stuff, recently had their Queboid Belgian IPA and it was outstanding.
Brewpubs are pretty rare it seems. I’ve not been to any and I’ve not heard anything about them really, but here are a few:
Duke’s Brew & Que supposedly has really badass BBQ ribs, and is home to Beavertown Brewery which brews on site.
Tap East - located out in Stratford.
Crate Brewery - Food seems to be good, beers are pretty unadventurous from what I’ve heard. Still working on some consistency issues as well, but they’re very new.
Porterhouse - brews on-site I believe, but it’s a chain as well and I’ve heard the beers are quite tame.