The new 5th, in which the next election will be held (assuming Rick Snyder signs the new redistricting maps) expands a bit.  It consists of Genesee, Bay, Arenac, Iosco, and parts of Saginaw and Tuscola counties.  The population of the district breaks down as follows.

60.3% Genesee
15.3% Bay
14.8% Saginaw
2.4% Tuscola
2.3% Arenac
3.9% Iosco

A number of candidates have expressed interest in running to replace Kildee.  As this is a democrat district, most of the action so far is on that side.

Former Genesee County Treasurer Dan Kildee, who is the nephew of the current congressman, has announced that he is running.  Kildee was treasurer from 1996 until he resigned in 2009 to become the head "of the Center for Community Progress, which promotes the reuse of vacant, abandoned and problem properties in cities and towns across the country." He very briefly ran for Governor in 2010 before dropping out.

Former Congressman and state senator Jim Barcia has said that he is "highly likely" to run.  Barcia was a state rep 1976-82, state senator 1982-92, and congressman 1992-2002.  After stepping aside for Kildee, he returned to the state senate from 2002 to 2010, when he was term-limited.  Barcia is a genuine moderate democrat who has an ACU life rating of 54%.  He is pro-life and a hunter who opposes gun control.  For conservatives, he would be a big improvement over Kildee.

State senator John Gleason has said that he is very serious about running.  Gleason was a state rep from Flushing before being elected to the state senate in 2006.  He is now in his second term, and would be term-limited in 2014.  Gleason is pro-life and has been endorsed by the NRA.

State Rep. Woodrow Stanley is "very interested" in running.  Stanley, who is black, was mayor of Flint from 1991 until he was recalled from office in 2002 due to fiscal mismanagement.  A state-appointed emergency financial manager was appointed afterwards.  Stanley was then elected to the Genesee county commission 2004-08.  In 2008 he was elected a state representative, and is now in his second term.  He would be term-limited in 2014.

Former lieutenant governor John Cherry has been mentioned as a possible candidate but has not yet expressed interest in running.  He was a state senator 1986-2002, rising to senator democrat minority leader before becoming lieutenant governor under Jennifer Granholm 2002-10.  He represented the suburbs of Flint.  Cherry is a liberal with strong union ties but is also pro-gun.

Genesee county treasurer Deb Cherry is the sister of John Cherry.  She also has been mentioned as a potential candidate but has not expressed interest in running.  She was a state rep before succeeding her brother as a state senator 2002-10 representing suburban Flint.  She was term-limited and was elected county treasurer in 2010, succeeding Dan Kildee.  Her political positions are similar to those of her brother.

There are plenty of other current and former legislators and county officials who could also run.

Here is the percentage of the new district that they have represented.

60.3% Dan Kildee
52.4% Jim Barcia (congress)
36.3% John Gleason
24% Deb Cherry (state senate)
14.5% Woodrow Stanley (mayor)

While this is a democrat district, it is possible for Republicans to win it under ideal circumstances.  For example, Rick Snyder won it in 2010.  Before that, John Engler and Candice Miller won it in 1998.  Against Kildee, Barcia, Gleason, or either of the Cherrys, Republicans would have no chance.  On the other hand, Republicans would have a good chance of winning if Woodrow Stanley were the nominee.  Even in majority-black Flint, he was recalled as mayor, and he is not likely to play well outside the city.

Republicans should have a credible candidate in case circumstances line up their way.  There are several Republican state legislators who represent significant portions of the district.  They are state senators Dave Robertson, Mike Green, and Roger Khan and state rep Paul Scott.  The portions of the district that they have represented are as follows.

31.6% Dave Robertson
20% Mike Green
14.8% Roger Kahn
15.2% Paul Scott

Robertson would be the strongest possible Republican candidate if he were to run.  This isn't very likely, though, as he was just elected to the state senate in 2010.  Green was also just elected in 2010 and lives in the part of Tuscola county that is outside the district.  Kahn is in his second term and would be term-limited in 2014.  He is from Saginaw township, which is split between congressional districts.  Scott is currently facing a recall campaign due to his efforts to reform teacher tenure rules in Michigan and doesn't seem likely to run.

Republican's best choice may be John Kupiec, who held Dale Kildee to only 53% of the vote in 2010, despite receiving very little attention.  He is considering running again.