A word of warning

The official ESTA website is https://esta.cbp.dhs.gov, and all visa waiver applicants should submit their information through this site alone.

However the American Embassy is warning travellers about rogue websites which have popped up alongside the official one, which offer assistance with ESTA for a fee. 

Authentic looking sites such as www.esta.us, www.esta.co.uk and www.travelauthorization.org charge unsuspecting visitors to the states as much as $249.95 (£165) for their application.

These sites have no affiliation with the US government and should be avoided at all costs. Unlike visas, where you may attend an interview and pay a statutory fee, visa waivers are completely free, and you shouldn’t have to fork out any money to obtain one.

It should be noted that, at this time (January '09), the official ESTA web site does not work with Google Chrome browser. On a PC stick with Microsoft's IE browser.