Visit the bike shops in your neighborhood. If a bike is made in the USA, that fact will be featured on a very large decal on the frame (as opposed to the teeny-tiny decals on the "Made in China" bikes). The companies with the widest variety of models that are made in the USA are Klein, LeMond, Gary Fisher, Trek, and Cannondale.
But, Cannondale is the only company making many models that sell for under $1,000 that are "Made In the USA". And, because Americans now have a Wal-Mart mentality, always looking for the cheapest price, no matter how cr@ppy the quality, it is doubtful that companies such as Trek and Cannondale will be making bikes in the USA ten years from now. Buy one while you still can.