for me its Bo Bice, Taylor Hicks, and Daughtry.
Both Bo Bice and Taylor Hicks have new albums now and both are on indie labels. They were dropped out of their RCA Record deal cause they refused to record the songs the management gave them to record and they refused to "pop" up their CDs.
so after the obligatory one album of poppier materials, they were dropped.
Bo Bice is now enjoying playing what he love best, countryfied southern rock while Taylor Hicks is now doing soulful countryfied southern rock.
Daughtry on the other hand accepted the offer to soften up his materials (his albums prior to American Idol is made up of really dirty guitar/post grunge rock 'n roll) and have it appealing to masses yet he never lose touch of the process. He still contribute to the production, song selection, and live show and is actually loving what he's doing.
These three are the only "Idols" i know who are really artists in their own right.