In the film "Ocean's Eleven" Rusty (Brad Pitt) says to Danny Ocean (George Clooney), "Off the top of my head, I'd say you're looking at a Bowski, a Jim Brown, a Miss Daisy, two Jethros and a Leon Spinks, not to mention the biggest Ella Fitzgerald ever!" What does it all mean?

He is referring to what types of con-men they will need to pull off the job. The terms are, I hear, actual slang used in the world of conning, though I can only find reference to "Ella Fitzgerald" meaning the con must be staged in advance. The others refer to specific types of con-men. I found a reference from TV Guide from an interview with the director, Steven Soderburgh. In it he describes making up the terms with the help of the screenwriter. They are a description of people and events needed to carry off the heist.

Carl Reiner's character, Saul Bloom, is the Boesky. That's Ivan Boesky, a hot-shot wall-street trader who got caught committing securities fraud. He's supposed to be a wealthy man to foot the bill who also has some inside information.
The Jim Brown is confrontation between Bernie Mac's character (Frank Catton, the inside man) and Matt Damon (Linus Caldwell) that is staged to distract. It is after a famous football (american) player who later went on to play leg-breaking thugs in a bunch movies. (Don't mess with me or you're in for it.)
The Miss Daisy refers to the SWAT van, their "getaway" vehicle. It comes from the movie, Driving Miss Daisy.
The two Jethros are "hillbilly gear-head types" to take care of Miss Daisy. They are Casey Affleck and Scott Caan (Virgil and Turk Malloy)
The Leon Spinks is the disruption of the boxing match, after Leon Spinks' famous surprise upset victory over Mohammed Ali.
And the Ella Fitzgerald is the tape they make and play in a loop in order to get into the vault. This is based on a Memorex commercial from the 70's in which a recording of Ella's voice breaks a glass and the quesiton is asked, "Is it live or is it Memorex?"