Via The Hill:

Sen. Olympia Snowe (R-Maine) will not run for reelection.

A top Snowe campaign staffer told The Hill that she will retire at the end of her term and would shortly be releasing a statement announcing her retirement.

The three-term senator was long expected to run for reelection, and had seemed to be gearing up for a run. She has not faced serious opposition in any of her runs for the Senate.

Her retirement means the Senate will lose one of its most centrist Republicans — one who often crossed party lines to work with Democrats, and acted as a bridge between the two parties. It is also a huge boon for Democrats: They had little hope of beating her, but become heavy favorites to win an open seat in the Democratic-leaning state.

So, I don’t follow Maine politics much, who will be the likely Republican(s), Democrat, and what are the prospects of holding the seat?

Update:  h/t reader Charles for this article, Snowe Fall(out):

Senator Snowe’s decision to not seek re-election is nothing short of a political earthquake that fundamentally changes the dynamic of every single federal race in Maine in 2012.  Both Democratic House Members, Chellie Pingree and Mike Michaud, will now be taking a look at a promotion to the Senate.