In an already crowded field, CourtListener, the newest free legal research website in town, impresses with its repositories of millions of legal opinions, thousands of judge reports (primarily directory type information), an audio collection of oral arguments, and millions of PACER documents and dockets.
That alone would be enough to garner attention, but adding to that, its advanced search options for the various databases it offers makes it even more outstanding.
Advanced opinion search:
Citation search using the official volume number, reporter and page number:
Advanced search of PACER documents and dockets:
Advanced Judge search:
Oral Argument Search:
All in all a resource worth exploring and using!