What makes Young's departure so intriguing is that he's one of just a handful of Republicans who represents a district Barack Obama won in 2012, in this case by a 50.1 to 48.6 margin. That makes Florida's 13th District the first truly competitive open seat of the 2014 midterms, and you can bet Democrats will fight hard to try to pick it up.
Right now, the only candidate in the race is attorney and former congressional aide Jessica Ehrlich, who ran against Young last year. While Young prevailed 58-42, that actually represented his weakest performance in 20 years. Ehrlich deserves credit for her willingness to take on a longtime office-holder no one else wanted to challenge, but with Young gone, there's a very good chance that better-known Democratic contenders will enter the race. (One perhaps slim possibility whose name came up a while back: ex-Gov. Charlie Crist, widely thought to be considering a gubernatorial comeback.)
Republicans, meanwhile, are losing an incumbent who was well-regarded and had successfully carved out a profile as a moderate. Given the state of the modern GOP, the party is likely to nominate someone more conservative, perhaps much more vocally so. The Tampa Bay Times suggests a few possible options, including former St. Petersburg Mayor Rick Baker, former Clearwater Mayor Frank Hibbard, Pinellas County Commissioners Karen Seel and John Morroni, and perhaps even Young's son, Bill Young II, who is just 29.
Regardless of who steps forward, this is going to be a serious contest, and as always, we'll be tracking it closely from now through Election Day.