In general, wills are public records, but that doesn't mean they're easy to track down. If the will is informal and has never been filed with a court, it's likely in the possession of a family member or hiding in a safety deposit box. If it has been filed, it should theoretically be available from a county courthouse, not many of which have records placed online. Many websites do, however, have collections of older wills, famous wills, and blank will templates.
Search for a specific person's will by calling the courthouse of the county where the person lived and asking if it has begun putting its records online.
Find blank wills and will templates for various circumstances at FindLegalForms.com.
Go to NationalArchives.gov.uk for a large directory of old wills from Great Britain dating from the 14th to the 19th centuries.
Find wills from famous individuals by doing a simple web search or going to the Famous Wills section of DoYourOwnWill.com.