Valid passports are required for entry by everyone except nationals of Canada. If you hold a EU passport or are a British Foreign national you will not require a Visa for a stay up to 90 days long. If you are going to be staying in the US for longer than 90 days or are intending to work in the US you will need to obtain a Visa from a local US Embassy. A list of all US Embassies is located on usembassy.org.uk, which also carries information relating to what kind of Visas are available and who is eligible. In general nationals of EU countries should have no problem obtaining the necessary documents.
In Britain US interests are represented by US Embassy in London, located at:
Embassy of the United States of America 24 - 31 Grosvenor Square London W1A 1AE Tel: 0207 499 9000
There is a large British presence in America, the Embassy is located at:
British Embassy 3100 Massachusetts NW Washington DC 20008 Tel: (202) 588 6500 or 588 7800. Fax: +(1)(202) 588 7850
In addition there are UK Consulates in New York, Atlanta, Anchorage, Boston, Charlotte, Chicago, Dallas, Houston, Kansas City, Los Angeles, Miami, Minneapolis, Nashville, New Orleans, Orlando, Phoenix, Pittsburgh, Portland, Puerto Rico, Salt Lake City, San Diego, San Francisco, Seattle and St Louis.