If you're considering writing an article for a legal publication, check out Information for Submitting Articles to Law Reviews & Journals.
This guide, compiled by librarians from the University of Missouri at Kansas City - School of Law, contains information about submitting articles to law reviews and journals, including the methods for submitting an article, any special formatting requirements, how to contact them to request an expedited review, and how to contact them to withdraw an article from consideration. It covers 202 law reviews. The document was fully updated in July 2011.
Update 8/9/11: A librarian at John Marshall Law School has also developed a Submission Guide for Online Law Review Supplements. This document contains information about submitting essays and articles to general online law review supplements. It will be updated on an annual basis and as law schools create new online law review supplements.
If you're at the submission stage, you may wish to use an online law review submission service which allows you to submit your manuscript to your choice of law journals simply by uploading the electronic file.
ExpressO, a fee based service from bePress, is well known and accepted by 750+ law school reviews. Many institutions, including the UW Law School, have an account through which faculty and staff can submit articles.
YIJUN Institute of International Law offers a free submission service called LexOpus. The system allows an author to submit a work to a number of author-selected law journals. An author may also, or instead, invite offers from any journal by choosing to indicate the work as open to offers.
Note that there are a number of law reviews which accept submission with ExpressO but not with LexOpus. See the list of LexOpus participating law reviews.