http://www.mayoclinic.com/health/hyp...-and-diagnosis

http://www.synthroid.com/Hypothyroidism/TSHTest.aspx

http://thyroid.about.com/od/thyroidb.../confusion.htm
From this link:

A major hitch in this connection of TSH to hypothyroidism and hyperthyroidism is an ongoing disagreement in the medical world. As of 2008, at most labs in the U.S., the normal reference range is approximately 0.5 to 5.0. So levels below 0.5 are considered possible evidence of hyperthyroidism, and levels above 5.0 would be considered possible evidence of hypothyroidism. There is, however, an ongoing, five-year dispute among thyroid experts, because as of late 2002, some endocrinologists believed that the range should be narrowed significantly, to 0.3 to 3.0. Endocrinologists have not yet reached agreement about a standardized normal reference range for the TSH thyroid test, despite the fact that they consider this test the gold standard test to use in diagnosing and treating many thyroid problems.

I know that I feel much better when my TSH is close to .3. I currently take 125 mcg of levothyroxine.