The Code of Federal Regulations (CFR) contains all US regulations arranged by subject. The List of CFR Sections Affected can be used to check that none of the sections has been superseded.
The Federal Register (FR) is published daily and contains all new regulations, as well as proposed regulations, notices of upcoming regulatory hearings, and executive orders.
Both annotated US Codes include references to related regulations, although the USCS often has more complete references.