Andrew Horne, retired Marine and Iraq war vet (of both Iraq wars, according to his bio) has announced his candidacy for the Kentucky senate seat. TPM has the announcement video, which never states a party affiliation. His web site, as far as I can tell, doesn't either. But a little googling showed that he's running for the Dem nomination to face McConnell in the general, and man does he seem tough in that video.
It's hard to know whether he's made a tactical decision to downplay party affiliation based on it being Kentucky that he's running in, or whether he made the decision because he's a Marine and military folks are discouraged from overt partisanship.
He's also a lawyer, so watch for McConnell's crew to start dredging up every case he's ever worked on if he gets any traction. Best of luck to him.