Casablanca has many great quotes. I think Claude Rains had most of the best lines.
"Round Up the Usual Suspects" is one of the most memorable and also the name of a great book by Aljean Harmetz about the making of Casablanca. It was published in 1992 so I'm not sure if it is still in print. It is a fascinating read about a film classic and the golden era of Hollywood. Any fan of that period should definitely try to get their hands on a copy.
Several of the non-American actors were actually refugees from Nazi Germany or occupied Europe. Conrad Veidt escaped from the Nazis but then found himself in Hollywood typecast as a Nazi villain. He had played a Nazi in Bogart's most previous picture All Through the Night.
Paul Henreid expected his role as hero Victor Laszlo to be given equal status as Bogart's character and resented the fact that it wasn't.
Due to wartime constraints, the production values were very poor compared with pictures made just a couple of years earlier such as Wizard of Oz and Gone with the Wind. The plane to Lisbon was a cheap prop and the set for Casablanca was borrowed from earlier Warner Bros pictures.
Contrary to popular belief, Ronald Reagan was never seriously considered for the film, nor was George Raft. The producer Hal Wallis apparently had Bogart in mind for the lead role from the beginning.
Personally, I love the film but over time I have lost respect for the Bogart character. I have come to see Rick Blaine as kind of a wimp for letting a woman get the best of him, even it it was Ingrid Bergman.