I have blog posts on the following of his films:
The Magnificent Seven (1960)
The Americanization of Emily (1964)
Our Man Flint (1966)
In Like Flint (1967)
The President's Analyst (1967)
FilmReference.com has a page on him where it says,
His versatility has allowed him to resist being typecast as an action hero, and Coburn's career is noteworthy for balancing lead and character parts. The common denominator of his roles is the character's air of confidence, often coupled with sophistication.
EW has a print interview here in which Coburn discusses The Magnificent Seven. Roger Ebert interviews him here. There are lots of photos here.