Here is an entirely subjective selection of Web sites* which you might find useful...

Outdoor activities accreditation

Adventure Activity Licensing Authority (AALA) (UK official body for adventure activities)
Grand National Archery Society (UK official body for archery)
Royal Yachting Association (RYA) (UK official body for sailing)

Resources in and around Tollesbury

English Nature (part of site local to Tollesbury)
Essex Wildlife Trust (owns local reserve)
Othona Community (retreat centre at Bradwell)
Royal Society for the Protection of Birds (RSPB) (owns local reserve)
Tollesbury (local information site)
Tollesbury (another local information site)
Tollesbury Mudclub (association of berth holders on Tollesbury's saltings)
Tollesbury Sailing Club (lively sailing site)
Tollesbury Saltings Ltd (TSL) (moorings, yacht repairs and engine sales)

Christian youth/music/arts/mission/compassion etc

Amos Trust (justice and hope for the forgotten)
Bar 'n' Bus (youth, schools and mission in Southend area)
Christian Aid (relief and development)
Christian Enquiry Agency (find out about Christianity, no strings attached)
Christian Information Network (a Christian er... information network)
Colchester Vineyard (local place for those not keen on religion)
Crossrhythms (music resource, festival, Web radio)
Delirious? (band)
Frontier Youth Trust (frontier youth resources, training and mission)
Greenbelt (arts and music festival)
Holy Space (online spirituality)
Labyrinth (more online spirituality)
Latin Link Step (mission to South America)
Network Youth (schools and youth work in Southend area)
Oasis (youth mission and service)
One Small Barking Dog (innovative media resources)
Rejesus (top site about Jesus Christ)
Ship of Fools (a magazine of Christian unrest)
Soul Survivor (youth congregations, conferences, music, mission)
St John's, Colchester (local church with lively youth programme)
Tastyfresh Music (music publishers, community, Web radio)
TEAR Fund (relief and development)
The Message (mission to Manchester, including The Tribe)
Tribal Generation (faith for Generation X and beyond)
UK Christian Handbook (the definitive guide to UK Christian organisations)
Youth for Christ (YFC) (youth mission and service)
Youth with a Mission (YWAM) (youth mission and service)

Other holiday/retreat venues and courses

Care for the Family (Strengthen Family Life)
New Christian Camping International (CCI) (guide to grouping of residential and outdoor centres)
New Hall (The Barn) (Catholic diocesan retreat centre, near Chelmsford)

Some Very Important Sites (Who put these in? – Ed)

Screwfix (from picture hooks to plasma cutters... awesome!)
Bad Human Factors Designs (yet more fearless revelations)

*FACT has no formal connection with any of these organisations (except TSL) and accepts no liability for the content of their Web sites.