Many states are moving towards some degree of legalization of cannabis.
The following states have legalized both recreational and medicinal cannabis to some degree (with links to the states' website with more information):
District of Columbia
The following states have legalized medicinal cannabis to some degree (with links to the states' websites for more information):
Westlaw also has a Marijuana State Legal Status Overview, which summarizes the current laws of all 50 states in more detail and provides a visual map.
Fox Rothschild, LLP has also created a very thorough National Survey on Marijuana Laws and Regulations, which may be a great starting place for finding the relevant laws if researching cannabis law in a specific state.