The National register of big trees 2004/2005 was just released: http://www.americanforests.org/resources/bigtrees/register.php.
The 889 "champion trees" in the US, classified by specy. You can get size and location, some of them have their pictures available on the site too.

The biggest tree in the US (as a matter of fact in the world) is still "General Sherman", a Giant Sequoia in California Sequoia National Park: Circumference: 1020 inches (25.9m), Height: 274 feet (83.5m), Spread: 107 feet (32.6m). No doubt very impressive, the largest living thing on earth. My favorite tree though is still the Live Oak (Quercus Virginiana), and the biggest one is located in Louisiana, here is its picture:

Circumference: 439 inches (11.15m), Height: 55 feet (16.7m), Spread: 132 feet (40.2m). Almost three times as wide as high!