The work of legal historians is eligible for consideration for a variety of prizes awarded by the Law and Society Association, including article and dissertation prizes. Descriptions of prizes are on the LSA website. Most unfortunately, the website does not have deadline information, or submission information. For that, you have to go to the LSA newsletter. Here's a link to the November 2006 newletter. Or go here, and click on November 2006. Then you need to scroll through the PDF file for award info. (I suppose the silver lining for your efforts is that if it's that hard to find, it limits the pool and increases your chances!)
The Article prize is for "exceptional scholarship in socio-legal studies for a journal article or chapter in an edited book published within the previous two years." The deadline is January 15.
The Dissertation prize deadline is TODAY! December 15, but is January 15 for year-end defenders. Go here for more info, and to the newsletter, here, for submission info.
The International prize deadline is January 31.
The deadline for Student Paper Prizes is February 1.
More information on the Hurst Prize in legal history was posted earlier on the Legal History Blog (deadline today!). Go here.