Tax Prof has an excellent round-up of resources on fellowships, Visiting Assistant Professor positions and more for aspiring law professors. It includes programs targeted to legal history, the Raoul Berger Visiting Fellowship in Legal History, Harvard, the Golieb Fellowships in Legal History, NYU and the J. Willard Hurst Fellowship in Legal History at Wisconsin.
Update: the Hurst Fellowship at Wisconsin no longer has a legal history focus. Details here.