Next year, someone not named Thomas Menino will be the mayor of Boston, for the first time in more than 20 years.

Menino, the longest-serving and first Italian-American mayor of New England's largest city, announced Thursday that he will retire at the end of his current term. At 70, the Democrat has been facing health issues, which he said have prevented him from keeping up his ideal pace.

Boston Mayor Thomas Menino. (Josh Reynolds/Associated Press) Boston Mayor Thomas Menino. (Josh Reynolds/Associated Press)

"Over the past few months, I have been weighing my own place in Boston’s bright future. During that time, I have been blessed to regain so much of my health. My physical therapy is going great. I feel better today than I have in a long, long while. I am back to a Mayor schedule, but not a Menino schedule,"  said the mayor, who was first elected in 1993.

Menino's decision to retire him means another marquee campaign in 2013. The field to replace him could grow quite crowded, and the mayor said he is not hand-picking someone to succeed him. At least a dozen names are in the mix, the Boston Globe reported.

At-Large City Councilor John Connolly had already announced he was running, even before Menino said he was stepping aside. A recent Globe poll showed Connolly trailing Menino badly. But an open race is a whole new world. And Connolly has the advantage of getting a head start on fundraising and building a campaign apparatus.

State Rep. Marty Walsh, who has strong ties to labor, recently said he would run if Menino did not. At-Large City Councilor Ayanna Pressley, an African American woman who is seen is a rising star, is another possibility, though she told the Globe, "I’m running for reelection."

A host of other names from the ranks of the City Council and state legislature could also end up running.(Boston Magazine has a good rundown here.)

Buckle up for another exciting off-year election! Below we rank the top five races of 2013. The marquee matchup with the most at stake is number one.

5. Massachusetts Senate (Democratic-controlled): The race for Secretary of State John Kerry’s old Senate seat has been pretty steady (read: boring) so far. Rep. Ed Markey continues to have an advantage on Rep. Stephen Lynch in the Democratic primary, with a recent poll showing Markey ahead by 11 points but 30 percent of voters undecided. Lynch also has better personal favorability numbers, so don't think the primary is over, despite Markey's many advantages. Whoever emerges will be a heavy favorite against a series of lesser-known Republicans, led by former U.S. attorney Michael Sullivan. (Previous ranking: 3)

4. Boston mayor (D): Some more food for thought in the campaign to replace Menino: The last open race for mayor in Boston was in 1983. In other words, open citywide races don't come along every day, which is even more reason to anticipate a crowded field of hopefuls. The preliminary election, from which the top two candidates advance to the general election, will be Sept. 24. (Previous ranking: N/A)

3. South Carolina 1st district special election (Republican-controlled): Things are getting really interesting in this race. While former governor Mark Sanford is hoping to advance from a Tuesday GOP runoff, Democratic nominee Elizabeth Colbert Busch has been preparing for the general election. Colbert Busch turned in a dominating performance in the primary last week, and she's proven she can raise money. It doesn't hurt her name ID that her younger brother is Comedy Central's Stephen Colbert, either. The 1st district is very Republican (nearly 60 percent voted for Mitt Romney in 2012), which means Colbert Busch is clearly the underdog against whomever she faces. But the consensus in the state is that Democrats prefer to run against Sanford over Curtis Bostic, because of the former governor's baggage. The real indicator of how close this race is will be if Democratic outside groups begin to enter the mix starting next week. (Previous ranking: 5)

2. New York City mayor (Independent-controlled): The favorite to succeed Mayor Michael Bloomberg (I), City Council Speaker Christine Quinn (D), is nothing short of interesting – and we’re not just talking about the fact that she would be the city’s first female mayor or its first openly gay one. Put plainly, Quinn is a character, full of colorful quotes and unafraid of labeling herself a “b----” or threatening people with castration (to put it mildly). The New York Times last week detailed her legendary temper, which she makes absolutely no apologies for. (Previous ranking: 2)

1. Virginia governor (R): We finally know what the matchup is going to look like here, with Lt. Gov. Bill Bolling (R) passing on running as an independent. Bolling succumbed to the reality that it would just be very hard to raise the money necessary to run without a party, even though early polls suggest he would have been formidable in a race between two polarizing figures. For now, the matchup between Attorney General Ken Cuccinelli II (R) and former DNC chairman Terry McAuliffe has all the makings of a pure tossup, and neither man benefitted from Bolling’s opt-out. (Previous ranking: 1)