From Modern Art Notes (Saltz is a VV critic, Tyler Green is the blogger at MAN)
Jerry Saltz: Very few artists have 30-year careers. Tyler Green: Way few. Partial list of American artists with consistent, ongoing 30-year careers: Johns, Rauschenberg, Twombly, Stella, Celmins, Eggleston, Thiebaud, Andre... (from Modern Art Notes)

I disagree with his choices:
Johns--we can exclude the 10 years of hatch work paintings from the 70s--his work is not consistent at all.
Rauschenberg--For Sure.
Twombly--Of Course.
Celmins--not on my list, but u nderstandable.
Eggleston--could i argue with this one...

Ones hes missing (since almost everyone on that list is a white male...)

Ed Ruscha
Richard Prince
Paul McCarthy
Jenny Holzer
Robert Bechtle
Kiki Smith
Faith Ringgold
David Hockney
Nam Jain Paik
Yoko Ono

I realise that some of these could not be considered american, and the time line might be a bit funny, and i agree wtih his central point, but the ones he left out seem political.