Links to Missouri government agencies, statutes, regulations, cases, etc. are posted by FindLaw and WashLaw. Primary legal materials are also available from Lexis, Westlaw and LOIS. Subscription services Versuslaw Fastcase have cases back to 1950; Google Scholar has cases back to 1950 for free. Supreme and appellate court cases are published in West's South Western Reporter.
You can look up the status of pending bills on the Missouri General Assembly website. For questions about Missouri legislation, call the Legislative Library at 573-751-4633 or send email to firstname.lastname@example.org.
Many areas of Missouri law are discussed in Missouri Practice, which is available in print and on Westlaw (MOPRAC).
The Missouri Attorney General posts AG Opinions back to 1968. Lexis and Westlaw have 1977-present. Older AG Opinions can be ordered from the AG's office by calling 573-751-3321 (they will send a PDF by email).
For information on Missouri legal materials, see the Introduction to Legal Materials posted by the Missouri Bar and the list of Missouri Practice Materials posted by the Washington University Law Library. For questions about Missouri legal materials, copies and/or inter-library loan, try calling the St. Louis University Law Library (314-977-2755) or the Washington University Law Library (314-935-6450).