To me, the most neck-snapping Republican endorsement of Obama comes from Charles Fried, the solicitor general under Ronald Reagan. To say Fried is an important legal figure in the pro-life world is an understatement.
As Solicitor General under Ronald Reagan, Fried was the one who argued that the court should overturn Roe v. Wade in Thornburgh v. American College of Obstetricians and Gynecologists .
In 1988, he went back to the court again as Solicitor General under George H. W. Bush and again argued that Roe be overturned, this time as part of Webster v. Reproductive Health Services.
In a letter to the McCain campaign, he asked that his name be removed from their legal advisory committee, explaining that the key reason “is the choice of Sarah Palin at a time of deep national crisis.”
I asked Professor Fried to elaborate on what, if anything, this says about Obama and abortion. He responded with this email:

There are many issues facing the country that are more important than what the President says or believes about abortion. I suspect that there are a great many things that Obama believes and will do with which I will disagree–starting with his judicial nominees, but in a time of economic and foreign policy crisis I found the risk of promoting to the presidency a person as ignorant and inexperienced as Sarah Palin–natural political talent though she is–unacceptable.

UPDATE: I’m told by pro-life friends that the Fried endorsement is less surprising than you might think because Fried has been “soft” on life issues for some time. He argued against Roe v. Wade as solicitor general because that was his job but was never personally pro-life and in 1995 said so.