The American Society for Legal History holds an annual conference in Legal History. In 2006 it will be held in Baltimore, and in 2007 in Phoenix. See their website:

For conference information. A Call for Papers is current for the Baltimore Conference.

Colleagues travelling to Europe next year might be interested in the European Forum of Young Legal Historians Conference in Frankfurt am Main
- call for papers is current to 31 January 2006, and their website can be accessed through the Institute of Historical Research website, which itself contains a variety of interesting conferences - after all, legal history doesn't just have to appear at special Legal History

This is a very nice site with historical conferences arranged by type of history, geographical area, and historical period, including a special legal history section.