If there are two House seats almost certain to flip from the GOP to the Dems this year it will be Joseph Cao (LA CD 2) and Delaware (At-Large). Cao pulled off a nearly miraculous win in 2008 in one of the most heavily Democratic districts in the country by beating scandal plagued (and now imprisoned) congressman William Jefferson. As long as the Democrats nominate a decent candidate they should prevail.
In Delaware Democratic Lt Governor Carney is a prohibitive favorite to win the open seat. Popular moderate Mike Castle is leaving the House to run for the Senate. He himself is a heavy favorite to win Joe Biden's old seat (if he does win, he'll be able to take his seat in November as soon as the election is certified, giving the GOP one more seat two months early) so both the Senate and House seats in Delaware will almost certainly flip parties this fall.
Charles Djou's House career may be only a few months long as he'll have to win again this fall after capturing 40% of the vote in Hawaii's special election last Saturday. Michael Barone thinks he can win a full term, and while I don't like to disagree with the godfather of American political prognostication, for Djou to win in HI CD1 will take an Sisyphian effort to pull it off.
Rob Portman, the popular Republican from Cincinnati who is running for the open Senate seat in Ohio, has looked surprisingly weak against his opponent, Lt Governor Lee Fisher. Ohio is slightly red and Portman is a strong candidate which should mean his poll numbers should be better than they are. While the GOP Senate candidates running for open seats in New Hampshire and Missouri seem to be pulling away for easy victories this fall, Portman will have to work hard to get his name out to win in the Buckeye State.