"Down With Love" (2003)
McGregor's never quite been praised for his comic chops, but he's got them in spades (every performance on this list shares a certain wit to them that few actors would have brought), and they received their best showcase in Peyton Reed's terminally underrated 2003 romantic comedy "Down With Love." A souffle-light tribute to the Doris Day/Rock Hudson comedies of the 50s and 60s, McGregor plays the excellently-named Catcher Block, a womanizing journalist who attempts to seduce writer Barbara Novak, a writer whose new book has caused a feminist storm in 1960s New York. Reed, who followed it up with the disappointing "The Break Up" and "Yes Man," nails the style, immaculately pastiching the Day/Hudson originals, and his cast are more than game: McGregor might be more Cary Grant than Rock Hudson, but he's enormous fun, and has oodles of chemistry with co-star Renee Zellwegger. The film tanked hard on release, crushed when released head-to-head with "The Matrix Reloaded," but it's become something of a cult classic since, and with good reason.