I really liked Woody Allen's Small Time Crooks. But here is a more "serious" list: http://thefederalist.com/2015/11/25/the-best-caper-movies-of-all-time/
Gotta be The Sting. Thief is a terrific movie, but I wouldn't categorize it as a caper flick.. I'd call it a neo-noir crime drama, but it's a GREAT movie.