I've attempted to build a very crude estimate of Barack Obama's performance on a district-by-district basis. I've given him 95% of the black vote, 60% of the Hispanic vote, 55% of the college white vote, and 35% of the non-college white vote. This gives him 43% of the overall white-plus-Asian/other vote, and just over 50% nationwide. I've then assumed that Black voters and Latino voters exhibit uniform voting patterns, and then computed the Partisan Voting Index among white voters to arrive at a number for Obama in the district This has obvious problems in districts that have a large number of illegal immigrants from Latin America, or in the three Cuban districts, but we can use some common sense to throw out these outliers.
Anywhere that Obama gets 45% of the vote or more, a strong local challenger has a shot at winning the district, especially if it's an open seat.
Districts that are currently on various lists of contested seats (Cook, Rotherberg, CQ, etc.) are in bold.
Unsurprisingly, most of the top open seats already have good challengers. The only real surprises are Dave Weldon's seat in FL-15 (Kissimme, Vero Beach) and Ray LaHood's in IL-18 (Peoria/Springfield), where Obama's home state mojo should provide an extra boost. With the right candidates, LA-6 and NM-2 might end up in play, but those are definitely at the edge of viability.