The teams with the longest championship droughts are 1. Cleveland Indians 2. Texas Rangers (Senators) 3. Houston Astros. I think the Padres may have won the World Series behind ace pitcher Kevin Brown back around 2000?
The Padres have made only two World Series appearances, losing to the Detroit Tigers in 1984 and to the New York Yankees in 2000. Thanks for reminding me of the Washington Senators/Texas Rangers franchise that has been in the American League since 1960 and has not won a World Series yet, losing to the San Francisco Giants in 2010 and the St. Louis Cardinals in 2011, making it the oldest MLB expansion team to not yet win a Series.
As a further note, the Pilots/Brewers franchise has made the Series only once (against the Cardinals in 1982) and the Expos/Nationals have never been to a Series yet.
Actually, the Yankees/Padres series was in 1998, as the 2000 World Series was the Subway Classic between the Yankees and the New York Mets.