Most states have a legal encyclopedia that summarizes the state's laws in considerable detail; an electronic edition is probably available on Lexis or Westlaw.
You may also want to check out a treatise on a particular topic (e.g., Witkin's California Evidence). You can locate these titles by searching the online catalog of a law school in the relevant state, or look up the topic in Searching the Law: The States by Francis R. Doyle (last published in 2003)
The topical "Reporters" published by BNA and CCH reprint the relevant laws from all states in a particular field, such as BNA's Labor Relations Reporter and CCH's Secured Transactions Guide. The Reporters are available in print as looseleaf services and through the publisher's subscription-based web sites. Some Reporters are available through Lexis and/or Westlaw.
Aspen's Corporations reprints each state's (C and LLC) corporate laws.
Finally, Lynn Hellebust's State Legislative Sourcebook provides in-dept information on how to find out about each state's legislature, legislative process, legislators, legislative histories, lobbying, newspapers, Registers, etc.
50-State Surveys: In addition to the resources discussed above, the following tools are useful when you need to know the law for multiple states on a particular topic.
(1) The National Survey of State Laws provides a state-by-state analysis of each state's laws in major areas (e.g., interest rates, age of consent, grounds for divorce, civil and criminal statutes of limitations, negligence, will, taxes, etc.), which is keyed to each state's statutes. The National Survey is available in print or on Westlaw (STSURVEYS).
(2) The Subject Compilations of State Laws, by Nyberg and Boast, lets you look up 50-state surveys on a wide range of topics. The Subject Compilation covers law review articles, judicial opinions, reliable web sites and the 50-state surveys available on Lexis and Westlaw. The annual volumes are available in many large law libraries, and subscribers can search the cumulative contents through HeinOnline.
(3) Over the years, the American Law Reports (ALR) series has published thousands of articles discussing the laws of multiple jurisdictions. Topics are typically chosen because of difference of opinion between state courts or a split in the Federal Circuit Courts. ALRs are available in large law libraries and on Westlaw.
(4) Lexis and Westlaw offer their own 50-state surveys compiling state statutory code or regulation sections on a particular topic. In most cases, the Westlaw surveys provide both citations and a brief description of each state's law, while the Lexis surveys provides only citations.
(5) Some of the BNA and CCH reporters, discussed above, include 50-state surveys. Note: The online editions of the CCH Reporters include "Smart Charts" that are essentially 50-state surveys, with direct links to the underlying laws and regulations.
(6) Subject-Specific Treatises. A number of treatieses are essentially 50-state surveys. These include the State by State Guide to Human Resources Law for employment law, Business Torts: A Fifty-State Guide (Aspen) and the Compendium of State Laws on Insurance Topics (see "National Association of Insurance Commissioners").
Historical Code Sections: Lexis and Westlaw have archived editions of most state codes back to the early 1990s. Fastcase goes back to the late 2000s. For copies of sections from older codes, call state or academic libraries in the relevant state ... or the library of the New York County Lawyers' Association (212-267-6646), which keeps historical volumes from the statutory codes of all states and D.C.
For more information, see "State Statutes and Codes," "State Regulations and Administrative Codes," and/or the entry for a particular state. For bill tracking, see "State Bills and Bill Tracking."