Rasmussen (12/15, likely voters, 9/21 in parentheses):
Robin Carnahan (D): 46 (46)
Roy Blunt (R): 44 (46)
Some other: 4 (2)
Not sure: 6 (5)
(MoE: ±4.5%)
If there's one thing everyone can agree on about the Missouri Senate race, it's been polling remarkably consistently; with the exception of a GQR poll from April, it's always been either a tie or a couple-point lead for Democratic SoS Robin Carnahan. That's partly because races are always close in deeply-polarized Missouri, and also because Carnahan and Republican Rep. Roy Blunt are pretty well-defined in voters' minds already. Look for these two to stay closely locked all the way through to next November -- although if you ask me, if there's one place where we might actually gain a Senate seat somewhere next year, it's here.
The two even have remarkably similar favorables: Carnahan's at 51/43, while Blunt is at 50/43. Barack Obama's approval is at 47/53 (with the requisite 1% unsure for a total of 101%), indicating that Carnahan's personal popularity associated with the family name helps her overperform the Democratic brand a bit.