Every state but California requires lawyers to graduate from an accredited law school and to pass the bar exam. In California, however, 60 college credits and 864 hours per year of correspondence law classes (not accredited) enable you to qualify to take the bar. After practicing law in California for five to seven years, you can then sit for the bar in other states.
No traditional law school offers law classes online.
While none are accredited (and thus not useful except in California), there are online law schools. Some of the better known schools include Concord Law School and the Abraham Lincoln University School of Law (see resource list for more).
The LL.M degree is a post graduate degree for those that have finished law school and want a specialization. These degrees are possible online, including from ABA-approved schools like NYU. More and more schools are putting LL.M degrees online.
Use the Online Law Schools Book to help you find the most current information on what law degrees and careers are available online.