The original constitutions of the original thirteen states are posted on the 18th Century Documents page of a historical documents Web site create by Yale Law School's Avalon Project. Other historical historical constitutions are posted by the NBER/Maryland State Constitutions Project; open the pull-down menu for"Select Constitution(s)" to see which constitutions are available. You can also find historical state constitutions included in the superseded volumes of each state's statutory code.
Current state constitutions are published as part of each state's current statutory code (see "State Statutes" and/or the entry for individual states by name.)
For a general discussion of state constitutions, see the Constitutions chapter of Fundamentals of Legal Research (West). For detailed analysis of each state's constitution, see the relevant title in the Reference Guides to the State Constitutions of the United States series published by Greenwood Press (e.g., The New York State Constitution: A Reference Guide).