CQ has produced a fascinating 2008 Election interactive grid which allows you to compare vote percentages for the presidential race with results of all U.S. House Districts.
Particularly interesting are the 34 House districts which elected or reelected Republicans while at the same time voting for Senator Barack Obama. The Ohio 12th is a perfect example of this. Republican Pat Tiberi was reelected easily to fifth term (56% to 41%) despite a 10 point margin of victory for Obama (54%-44%).
There were also a number of House districts that went to Senator John McCain which Democrats easily carried, most of them being in the South and West. The Utah 2nd is a good example of this phenomenon. Democrat Jim Matheson, first elected in 2000, easily won reelection by an almost 30 point margin (63%-35%) while McCain rolled 58% to 40%.
As Taegan Goddard at Political Wire warned, "be prepared to spend a lot of time clicking around."