Not a huge fan of the Sheffield signing, though it does bring about a good trivia question... Gary Sheffield has 11 career walk-off hits. We're gonna factor out Willie Mays and Duke Snider because available data (from the likes of Baseball-Reference and MikeMav.com) begins in 1954. Among all those others who have played for the Mets, who has the most career walk-off hits, with 19? The answer: Rusty Staub. Here's a more thorough list with help from MikeMav
A blog devoted to cataloguing New York Mets walk-offs and other trivia. For those unaware of the definition of walk-off just replace the term with the words "game-ending" and you should have a much better understanding of the phrase.