With the Census Bureau having recently released its 2008 population estimates, organizations like Election Data Services have revised their estimates (.pdf) of which states are likely to gain or lose seats in the Congress following the reapportionment triggered by the 2010 Census. Seats gained in the Congress, of course, also mean seats gained in the Electoral College.
In general, migration into the South has slowed down slightly. As recently as a year ago, it appeared almost certain that Florida would gain two seats in the reapportionment and North Carolina would gain one. But now, it looks that Florida may only gain one, and North Carolina might not gain any. The seats being "saved" are those in the Northeast and the Midwest. Whereas it appeared at one point, for instance, as though New York and Pennsylvania would each lose two seats, they may now lose just one each.
Migration into the West, unlike the South, has not really slowed down any.
Keep in mind that the interim population estimates released by the Census Bureau are not nearly as comprehensive as the actual, decennial Census; as such, these estimates should be treated as having fairly high margins of error. In addition, the Census itself has a fairly high margin of error depending on things like what sampling procedures are used how effective the
Census is at accounting for illegal immigrants.
It is nevertheless clear that, on balance, blue states are losing population and red states are gaining it; a net transfer of somewhere between 5-10 electoral votes should occur between blue states and red states as based on the 2000/04 electoral map. It should be kept in mind, however, that the same factors that are causing red states to gain population from blue states are also making red states more purple. It's the new residents in North Carolina, for instance, most of whom game from the East Coast, who allowed Barack Obama to win the state in November. Furthermore, Congressional appointments must not only be balanced for population between the different states but also within a given state. While Texas will probably gain four seats, for instance, if those gains come in relatively blue parts of the state like South Texas and the Dallas-Fort Worth metroplex, it might not hurt the Democrats very much.
A rundown of the states likely to gain or lose seats follows.
States gaining seats:
Arizona appears to be locked into gaining two seats, although there is an outside chance it could be held to just one.
Florida originally appeared on track to gain two seats, but more recent estimates have it gaining one instead.
Georgia will almost certainly gain exactly one seat.
...likewise, Nevada will gain a seat.
North Carolina may gain one seat, or it might not.
Oregon is about even money to gain a seat.
South Carolina is better than even money to gain a seat.
Texas will gain at least three seats, and will probably gain four, although a slowdown in migration could prevent that.
Utah will definitely gain a seat.
Washington might gain a seat.
States losing seats:
California may lose a seat, although the most recent estimates show that as being less likely. Another significant factor with California (and Texas, Florida, etc.) is how efficient the Census is in accounting for illegal immigrants, who like it or not do count toward Congressional appointments.
Illinois will probably, although not certainly, lose one seat.
Iowa will definitely lose a seat.
Likewise, Louisiana will lose one (thanks, Hurricane Katrina!)
Massachusetts will also lose a seat.
...as will Michigan (thanks, failing domestic auto industry!)
Minnesota will probably lose a seat, although it might be able to prevent that.
Missouri, likewise, will probably, although not certainly, lose a seat.
New Jersey will lose a seat.
New York, which previously appeared in peril of losing two seats, now may lose just one, although it may be pretty close if people migrate out of the state following the financial sector collapse.
Ohio is locked in to losing two seats.
Pennsylvania will lose one seat, and is not completely out of the woods for losing a second.
So to summarize:
Arizona +1 or +2
California 0 or -1
Florida +1 or +2
Illinois 0 or -1
Minnesota 0 or -1
Missouri 0 or -1
New Jersey -1
New York -1 or -2
North Carolina 0 or +1
Oregon 0 or +1
Pennsylvania -1 or -2
South Carolina 0 or +1
Texas +3 or +4
Washington 0 or +1
See also: Swing State Project.