An institution, and for good reason. If you're not going on a tour, the bar is pretty great, and normally has a good street food stand (whether it's pizza or toasties) outside.
Tours: There are two options. A pre-booked tour is in-depth and costs £12. It includes several beer tastings, as well as a chance to try some beer from the tank. A drop-in tour is more casual, and the fee is donated to a Camden charity.
Nearest station: Kentish Town West
A friendly Hackney brewery with a great range of bottled ales. (My favourite is the Hook Island Red.)
Tours: A tour costs £12 and includes a tasting of four beers (Five Points Pale, Hook Island Red, Railway Porter, and Five Points IPA.)
Nearest station: Hackney Central
If you're a fan of craft spirits, this elegant distillery is for you. The ELLC produces small batch gin, and vodka, and they also import their own rum and bitters.
Tours: There are two options. The Distillery Tour costs £35, and includes four complimentary spirit tastings (split between gin and vodka). The Gin Lover's Tour costs £55, and includes eight complimentary tastings (including one vodka).
Nearest station: Bethnal Green or Mile End
Meantime offers a tremendous London lager, as well as more interesting things like a raspberry wheat beer and chocolate porter.
Tours: Tours cost £20 per person (except on Monday–Thurs and Sundays, when it's slightly cheaper at £17.50 per person) and include a "tutored tasting" of a selection of Meantime beers.
Nearest station: North Greenwich
Dating back to 1828, Fuller's knows what it's doing. I mean, check out the brewery shop.
Tours: It's £10 for a tasting tour, or £7 for a non-tasting tour. The tasting one includes "a tutored tasting of some of Fuller’s finest ales". Be aware that tours only run Monday–Friday.
Nearest station: Turnham Green
8. By the Horns
Small-batch ales, brewed with love. In case you're interested, they also use open-top fermenters.
Tours: There are two options. A taster tour costs £10 per person, and includes three 1/2 pint tasters. A full tour costs £15 per person, and includes three pints (or bottles) of beer.
Nearest station: Tooting Broadway
If you're interested in the history of both London and gin, and you want to see how big-batch gin is made, this is your chance.
Tours: A tour of the distillery costs £12, and includes a gin and tonic.
Nearest station: Kennington
10. Sambrooks
This small Battersea brewery really punches above its weight, and has some firm fans because of it.
Tours: There are a couple of options. There is a informal open evening once a month. You can also book a private tour, including a free tasting. Both options cost £15 per person. For the super-keen, Sambrooks offers a "Brewer for a Day" experience.
Nearest station: Clapham Junction
London's oldest micro-brewery, with some pretty nice seasonal ales.
Tours: Tours cost £15 per person and are pretty good value – you get three pints and a glass to take home.
Nearest station: Strawberry Hill
Did someone say "small-batch artisan gins right in the centre of London"? Then roll up, roll up.
Tours: There are two options. A daytime tour costs £10 per person, and includes a gin and tonic. An evening tour costs £25 per person, and also includes tasting of three gins.
Nearest station: Blackfriars
13. Wild Card
A small local brewery in Walthamstow. The head brewer has a background in chemical engineering, so it deserves its reputation for "no-nonsense, uncompromising beers".
Tours: Tours cost £25 per person, and include a tutored tasting and four half-pints, as well as a T-shirt.
Nearest station: Walthamstow Central
14. Shepherd Neame
If you don't mind travelling to Kent, you can visit Britain's oldest brewer (est. 1698!).
Tours: A comprehensive tour costs £12.75 per person, and includes a tutored tasting of Kentish ales and speciality lagers.
Nearest station: Faversham (about an hour from King's Cross).
London's first whisky distillery since 1903, and it also produces the splendid Dodd's Gin as well as more experimental spirits.
Tours: Tours cost £15 per person, and include a cocktail and gin samples.
Nearest station: Clapham Junction
16. London Beer Lab
If you've ever wanted to brew your own beer, but didn't know where to start, the Beer Lab is here for you.
Tours: A one-on-one session costs £80, and you will brew four different recipes with a brewer. You can then return a few weeks later and take home 12 bottles of the beers you helped brew. Or, a session for three people costs £160 in total and you will make 20 litres of beer, and you can then return later, learn how to bottle it, and bring it home.
Nearest station: Brixton
17. The Ginstitute
Have you ever wanted to create your own bespoke bottle of gin? Now's your chance. Attend the Ginstitute.
Tour: A history lesson, a tutored tasting, and the chance to create your own unique bottle of gin. It's not cheap, at £100 per person, but you get a lot of bang for your buck: A cocktail reception, a class at the Ginstitute, a 70cl bottle of Portobello Road gin, a 70cl bottle of your own bespoke gin, and a martini at the end.
Nearest station: Ladbroke Grove
H/T to Clare from Beavertown Brewery for some of these suggestions.