This is a list of countries in the Visa Waiver Program as of October 2012 as follows:
Travelers from these countries may visit the USA for tourism or business without a visa and may stay for up to 90 days. They must first receive authorization through ESTA (Electronic System for Travel Authorization). All persons traveling on the VWP must have a machine-readable passport. The passport must be valid for at least 6 months beyond your intended stay.
Short trips to Canada or Mexico do not restart the 90 day clock. This means you can’t make a quick trip to Canada or Mexico to restart your 90 day visit.