From The Virtual Chase:
- U.S. Party/Case Index
- Legal Dockets Online
- Cornell Legal Information Institute
- GPO Access
- Full-text State Statutes and Legislation
- Electronic Discovery Law
- The Bluebook
- BRB Publications Inc.
More detail at the site. To me, the most useful is Cornell’s LII — it’s the fastest, most intuitive form of Federal law available anywhere, and it’s free (donations are encouraged). I use it all the time.
The remainder are largely investigative tools; they’re great when you need them, but it’s really not that often.