The Legal Writing Handbook by 
Universal Citation Guide, Edition 2.1 by 
The Bluebook: A Uniform System of Citation by Online citation tools can help with Bluebok style formatting. Zotero and Mendeley (both free) are known for being fairly reliable; however, as with all online citation tools, the accuracy varies and it is always best to double-check against the actual guide.
This page was adapted from http://libguides.tulane.edu/citation and used with permission from the Howard-Tilton Library/Tulane University.