The Thames Discovery Programme - for guided walks on the Thames foreshore http://www.thamesdiscovery.org/
The Thames Explorer Trust – for guided walks on the Thames foreshore http://www.thames-explorer.org.uk/about/
The Port of London Authority - https://www.pla.co.uk/Environment/Metal-Detecting-and-Digging-on-the-Thames-Foreshore
Information on the Portable Antiquities Scheme https://finds.org.uk/
The Museum of London http://www.museumoflondon.org.uk/london-wall/
Bowl of Chalk http://www.bowlofchalk.net/For fantastic bespoke guided walks in London, and... best of all, you can "pay what you want". I recommend Bowl of Chalk (cockney rhyming slang for walk). You can't go wrong!
http://www.adrianbroughpottery.co.uk_ - A very talented potter based in Lelant, near St Ives in Cornwall, who also happens to run a splendid b&b, with the possibility of sea kayaking, pottery courses, great food etc... well worth the visit.
Jay Ouellette, visual artist from Canada. I particularly love her sculptures of birds made from driftwood.
http://seaglassartists.ning.com/ site with some great sea glass artists
http://www.thamespics.co.uk/about-thamespics-co-uk/ some great pics of comings and goings along the River Thames.