Worker's compensation laws are published in each state's statutes (see "State Statutes") as well as in the State by State Guide to Human Resources Law.
Lexis has a database for all Federal and state cases and administrative decisions (WCSSD;WCCASE), all Federal and state cases (WCSSD;MEGAWC); all Federal cases (WCSSD;FDCTWC), all state cases (WCSSD;STCTWC), all state administrative decisions (WCSSD;ALLWRK), cases from individual states (WCSSD;xxCTWC), administrative decisions from individual states (WCSSD;xxWORK), etc. Lexis also has Larson's Workers' Compensation Laws (WCSSD;LARWCL) and about ten state-specific treatises including the New York Workers' Compensation Handbook (WCSSD;NYWCHB) and California Worker's Compensation Law (WCSSD;CALCOM).
Westlaw has a database for the Federal Workers' Compensation-Benefits Review Board decisions (FWC-BRB), each state's Workers' Compensation Law Reporter (xx-WCLR, or WCLR to search all states at once) and each state's workers' comp administrative decisions (xxWC-ADMIN, or MWC-ADMIN to search all states at once).