Carhartt boots were made by Red Wing from 2004 to 2011. Now they are made by Black Diamond, who I know little about other than make a lot of protective boots for fire fighters. I had a pair of the Red Wing made Carhartt boots and they were good but not great. The sizing was a bit off and they were closer to Red Wing's Worx line as far as quality.
Like ac700wildcat I have had positive experiences with Red Wing and Danner (USA made). I also like Chippewa boots and am wearing a pair of their Service boots at the office today although that style is just too pretty to be used as a real work boot.
I recently bought a pair of Danner's USA made Quarry boots and they are an excellent combination of comfort, support and durability. I appreciate the fact that Danner is upfront about which boots are made in the USA and which are not. I have had good experiences with Danner's non USA made boots but my preference is the USA made and that has more to do with patriotism than quality expectations.