The National Conference of State Legislatures is a great resource on election laws in all 50 states.
NCSL resources include:
- Comparisons of laws as to different facets of the election process.
- Profiles of each state
- Pending legislation in all states
The Massachusetts profile is a handy reference for Massachusetts laws.
An additional good source is the federal Election Assistance Commission.
If you want to share other resources, please feel free to do so in the comments!