Green Arrow
Justin Hartley played the Green Arrow in seasons six and seven. By season eight though, he was a regular cast member instead of just in a recurring compacity. Producers said that Hartley was their first choice to play Oliver Queen.
Batman
Originally Tollin/Robbins Productions wanted to do a show about a young Bruce Wayne. However Warner Bros. wanted to do an origin movie for Batman, they didn’t want to compete with a series. Tollin/Robbins then approached Peter Roth, president of Warner Bros. Television, in 2000 about doing a series on a young Superman. Alfred Gough and Miles Millar developed a pilot which was based on the film Eraser. Once Roth watched the pilot, he approached Gough and Millar about doing the pilot about a young Superman. Thank goodness!