| How about Mike Pence? From the Politico:
House Republican Conference Chairman Mike Pence (R-Ind.) will speak with aides this afternoon to discuss whether to jump into the Indiana Senate race. [...]
But aides are skeptical he'll pull the trigger. There are concerns that he publicly passed on the opportunity to run last month, citing the GOP's strong position in the House. Further, he's considered among the strongest candidates for governor of Indiana in 2012.
Privately, aides to Pence say he was concerned about Bayh's $13 million in the bank, but now Pence could be able to "walk into the seat," according to an aide.
I find it hard to imagine Mike Pence actually doing this -- the mechanics seem to be too difficult to pull off with the filing deadline so soon. That said, the rumors are swirling; we're even hearing some chatter about Gov. Mitch Daniels plunging into the race.
For the Democrats, speculation seems to be centering on current Reps. Brad Ellsworth and Baron Hill, ex-Rep. Tim Roemer (the current Ambassador to India), and Evansville Mayor Jonathan Weinzapfel, who is viewed as one of the party's leading candidates for the gubernatorial race in 2012. But of course, Democrats may need to make sure that the ballot is clear before getting the opportunity to hand the nomination over to any of these guys. (And, as it stands right now, that's an open question.) Otherwise, we may be looking at a Charlie Wilson-style write-in campaign.
UPDATE (Crisitunity): So what about Tamyra d'Ippolito, college-town coffee shop owner and erstwhile Senate candidate? TPM contacted her camp and finds that she's currently 1,000 votes short of the required 4,500, with a particular shortage in IN-08 (she needs at least 500 in each congressional district). Somehow, given the choice between running her or naming their own preferred candidate, I don't think the party will get actively involved in the efforts to help her to get on the ballot in time. Neither does d'Ippolito: "So I have no idea what they will do, but they have not been cooperative so far," d'Ippolito added. "It would be nice if they turned around and became cooperative, but I don't know."
UPDATE: It's now sounding like Mike Pence won't run, despite an hour or two of interest. Chris Cillizza tweets that Pence's spokesman's official statement is: "Mr. Pence has filed for re-election to the 6th Congressional District of Indiana." Which apparently is code for "no."
LATER UPDATE (James): d'Ippolito's campaign manager has told Real Clear Politics that their chances of getting all the required signatures are "slim to none", but that they won't step aside if they somehow do.
YET ANOTHER UPDATE: Cross former Democratic Governor Joe Kernan off the list; he says he won't run.