The following sites provide access to US Circuit case law.
UScourts.gov provides excellent information *about* (and from) the Judicial Branch of the U.S. Government. Although you can find cases here (via Pacer), you will need to register and potentially also pay a fee. Search for US cases using the links provided in the surrounding boxes.
Image source: Donna Brickley & IT students, LVC. c2011.
Geographic coverage areas of the United States Circuit Courts of Appeals below. Access a dynamic version of the map here, as well as links to US Circuit Court websites.