From The Virtual Chase:

1. U.S. Party/Case Index
2. Justia
3. Legal Dockets Online
4. Cornell Legal Information Institute
5. GPO Access
6. Full-text State Statutes and Legislation
7. Electronic Discovery Law
8. The Bluebook
9. BRB Publications Inc.
10. ZoomInfo

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.