In Missouri, we currently hold MO-1 (Clay, solid Dem), MO-3 (Russ Carnahan, likely Dem), MO-4 (Skelton, leans Dem, but only because he holds the seat, else likely Repub.), and MO-5 (Cleaver, solid Dem).
That leaves MO-2 (Akin), MO-6 (Graves) , MO-7 (Blunt), MO-8 (Emerson), and MO-9 (Hulshof). Akin's district used to be a suburban St. Louis swing district but got much more Republican in the last round of redistricting (its like 60% GOP now, IIRC). If we were ever to win Blunt's district, we'd have won 400 other districts along with it. Emerson is too smart and moderate of a pol to lose. So, that leaves Sam Graves's MO-6 and Kenny Hulshof's MO-9.
The 9th was held for 20 years by conservative Democrat Harold Volkmar until he was defeated by Kenny Hulshof in 1996 (strange, given that '96 was a good Democratic year). The 6th District was held by Democrat Patsy Danner until 2000 when she retired due to breast cancer. Her son narrowly lost to Sam Graves, 51-49, in 2000.
Hulshof is widely considered to be a stronger incumbent than Graves and is rumored to be considered the likely Republican candidate for either Kit Bond's Senate seat after he retires or a possible replacement for the abysmally bad Matt Blunt in 2008. Graves, on the other hand, does not have nearly as high a profile as Hulshof.
Of the two districts, the 6th is slightly more Democratic than the 9th, but I believe that the 9th is considered to have stronger Democratic roots.
Finally, the best time to take a shot at these might not be this cycle. In 2008, there will be no Senate race in MO, and the much reviled Matt Blunt will be up to get his ass kicked, plus there should be a strong level of GOP fatigue in the state by then.....