Tom Paine's greatest hits
Continuing Brad Delong'sIndependence Day Tribute to Tom Paine, here are some more links to free, full-text editions of Paine's work.
Brad already linked to Paine's revolutionary pamphlet, Common Sense.
Anyone who says that the Founding Fathers envisioned a Christian nation hasn't read The Age of Reason:
It is upon this plain narrative of facts, together with another case I am going to mention, that the Christian Mythologists, calling themselves the Christian Church, have erected their fable, which, for absurdity and extravagance, is not exceeded by anything that is to be found in the mythology of the ancients.
Also see Paine's The American Crisis, 1780-1783, the source of the famous quote:
THESE are the times that try men's souls. The summer soldier and the sunshine patriot will, in this crisis, shrink from the service of their country; but he that stands it now, deserves the love and thanks of man and woman.