Not by any stretch of the imagination a complete guide to graf in London, but it does cover the most popular spots across the capitol.

To visit all these places would take at least two full days of travelling (remember to take an A-Z), so be prepared. If you're purely after photos, then I suggest visits Westbourne Park, Tufnell Park, Barking and Plaistow. If your painting then Westbourne Park, Camden, Tufnell Park and Unity will get you good exposure - but your piece may not last long.

 Westbourne Park
There are three main places to visit around here, but it's actually worth walking parallel with the A40 from Westbourne Park, through Royal Oak and right up to Paddington Station. The whole area is battered with tags and dubs. Pay special attention to the wasteland behind the car pound near to Paddington Station.

Nearest station: Westbourne Park on Hammersmith & City Line
Location: Playstation Park - Turn right out of the station and take the first right. Head down until you reach the pub on the right hand side, and turn right over the footbridge (as seen in Spraycan Art) by the pub. Once you are over the bridge you are under a flyover, turn left & you are there. It is a skatepark right next to the tube tracks in which boards and flyover supports are painted. Look for the gaps in the fence or ask permission to come in. If they ask for an entrance fee, tell them to fuck off.

The Pit - It is situated on Wornington Road near the junction with Goldbourne Road. It is in a Basketball court set below pavement level.
Comments: 'The Pit' was London's first ever Hall of Fame, and is supposedly, still, it's premier one, but activity here has been sporadic recently. The area is very unsettled, so keep your valuables safe and don't be surprised if you encounter problems.
Photos:  DJ Archive - [ 1 | 2 | 3 ]
N-igma - [ 1 | 2 | 3 | 4 | 5 | 6 | 7 ]
 Fulham 'Unity'
Nearest station: Hammersmith, on the District, Piccadily, Hammersmith & City Underground lines. Or Fulham Broadway, on the District Line.
Location: Caroline Walk. Behind the pub at the roundabout at the junction of Lillie Road, Munster Road & Dawes Road.
Comments: Once the site of the annual Unity jams, this plot has seen some of London's best pieces in recent years as it has some of the best wall space in London. More recently you are more likely to find dubs & throw-ups there than anything else.
Photos:  DJ Archive - [ 1 | 2 | 3 | 4 | 5 ]
N-igma - [ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 ]
Nearest station: Camden Town Underground on the Northern Line. Camden Road BR on North London Line.
Location: A play area between Clarence Way & Hawley Road.
Comments: With lots of small panels and a few larger surfaces to paint on, this has to be one of London's most popular HoF's. Unfortunately it attracts a lot of trouble, as pieces get dissed and people get robbed. Writers visiting from out of town may not be welcomed by local writers. Sometimes used as a car park on Sundays.
Photos:  DJ Archive - [ 1 ]
N-igma - [ 1 | 2 | 3 | 4 | 5 | 6 | 7 ]
 Tufnell Park
Nearest station: Tufnell Park Underground on the Northern Line.
Location: Follow Tufnell Park Road almost to the very end. As the end approaches (just past a church on a corner) on the right is a housing estate. The wall is in here (set back off the road) in a children's play area.
Comments: This has to be one of the best known legal spots in London. The main wall is generally used for colour action and productions, and the side walls are normally covered in dubs.
Photos:  DJ Archive - [ 1 ]
N-igma - [ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ]
 Grove Park
Nearest station: Grove Park or Lee. Both British Rail with trains running from London Bridge.
Location: In Northbrook Park, on Baring Road, which runs between the two stations.
Comments: This is quite a small wall (6ft x 100ft) and is a bit out of the way. Once a favourite location for piecers, but more recently it's been dominated by bombing and dubs. It's legaility is now in question.
Photos:  DJ Archive - [ 1 ]
N-igma - [ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 ]
 Crouch End
Nearest station: Crouch Hill BR on Silverlink Metro service between Barking & Gospel Oak. Or catch a W7 bus from Finsbury Park Tube & BR station.
Location: In the Crouch Hill Recreation Centre. Just as Crouch Hill gets really steep it goes over an old railway bridge, the centre is just to the left of this bridge. The best walls are below the bridge, with some short walls around a football pitch up by the buildings
Comments: This is a very quiet spot, with not much being painted here. Though what is painted is usually quite a high quality, especially under the bridge.
Photos:  DJ Archive - [ 1 ]
N-igma - [ 1 | 2 | 3 ]
Nearest station: Plaistow/West Ham, on District Underground line.
Location: On the only bridge over the train tracks between West Ham & Plaistow stations. Follow the 'Greenway' footpath that runs parallel with the tracks from West Ham, or if coming from Plaistow, walk back along parallel with the tracks through the housing estate until you get to the bridge.
Comments: Known as the East London or AWE HoF, it can be a great place for getting photos.
Photos:  DJ Archive - [ 1 ]
N-igma - [ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ]
 New Malden 'The Cut'
Nearest station: New Malden BR - trains from Waterloo
Location: Along a footpath that runs parallel with the tracks and Acacia Grove. Exit the station and cross over the High Street at the traffic lights. Walk along the footpath directly ahead of you for about 100 metres.
Comments: Once legal, the council have made a u-turn and it's now technically an illegal spot. Action occurs, but it's mostly quick silvers and dubs.
Photos:  DJ Archive - [ 1 ]
N-igma - [ 1 | 2 | 3 ]
Nearest station: Barking Tube & BR station. On District Line, Hammersmith & City Line and BR's out of Fenchurch Street.
Location: On the concrete pillars that support the A406 where it crosses over the train tracks. Turn right out of the station & take the first right. Go all the way down, pass between the flats and go through the subway under the bridge. Follow the alleyway that runs by the tracks onto the short road and continue to the first junction. Turn right then take Crows Road, which is the first left. At the end of Crows Road is a children's playground and from there you will see a blue bridge over the river. Over the bridge, then turn right and follow the river up. You will see the flyover in front of you.
Comments: Lovely walls, but rarely painted. The legality is a bit ambiguous.
Photos:  DJ Archive - [ 1 ]
N-igma - [ 1 | 2 ]
 Kew Gardens 'Grundy'
Nearest station: Kew Gardens Underground on the District Line and BR main line.
Location: An abandoned warehouse and outbuildings set amongst some trees next to the River Thames, behind the Public Records Offices
Comments: Dark and moody warehouse full of pigeon shit. Popular with local writers and crews from West London. Very hard to get photos due to the poor light conditions.
Photos:  N-igma - [ 1 | 2 ]