A state-specific law encyclopedia (e.g., the Maryland Law Encyclopedia) can be a good starting point for a research problem set in a specific state.
General coverage law encyclopedias (American Jurisprudence 2d or Corpus Juris Secundum) can provide general background and citations to primary authorities from various states.
The state series of A.L.R. may contain an annotation on your topic. A print index covering the third through sixth series is available, or A.L.R. can be searched on Westlaw.
Many treatises or the Restatements of Law can provide analysis and citations to state case law.
Law reviews can sometimes be found dealing with the law of specific states. Westlaw and Lexis provide databases that cover legal periodicals published by law schools in individual states; search these with some caution because they frequently include only a few publications. Also helpful are multi-state survey articles in law reviews which help identify trends and put the law of your state in perspective.