According to Whipcongress.com, Senators Daniel Akaka, Byron Dorgan, and Jon Tester, have stated their support for a public option through reconciliation.
This brings the number of signatories up to 40. With Tom Harkin, Herb Kohl, and Claire McCaskill as definite "maybes," 50 votes in the Senate is starting to seem plausible. Of course, given ongoing vote troubles for Democrats in the House, that chamber needs to be monitored and whipped at least as closely in any public option campaign.