There are many thousands of organisations which you might find useful - here are some of the more obvious ones!

UKBA (for informaiton on visas)

Transport for London (information on travel in London on buses or the tube)

National Rail  (information on train travel through the UK)

Oyster (for travel on the tube and buses)

Time Out (information about what's in in London)

British Council (information about studyign in the uK and also general advice on cultural life in the UK)

English UK (the association for all Accredited English Language Schools)

CILT (the National Centre for Languages - modern foreign languages)

BBC (lots of information on whats on and a summary of the news)

Cambridge ESOL (for Cambridge exams - First certificate / Advanced)

Westminster University (our usual ielts centre)

IELTS (the main site for information on ielts)

Edexcel (for workskills qualifications)

Schengen visa application (if you want to apply for a schengen visa to travel in Europe)  

Google Maps

English page (grammar exercises)

English plus (grammar exercises)

Vocabulary.com (vocabulary exercises)

Ask Oxford (online version of the Oxford English dictionary)

Etymonline (etymologies of Enlgish words)

Guardian (newspaper)

Times (newspaper)

Independent (newspaper)

Lyrics (words to songs)

FloJoe - exercises for Cambridge ESOL exams

Gumtree (accommodation and jobs in London)

Visit London (information about what's going on near your tube station)

Hotcourses (evening courses in London)

Up My Street (information about services in your neighbourhood)