Below are a few suggestions to get you started. REI offers many books on where to snowshoe locally, plus you should consider local clubs or the taking a class with the REI Outdoor School.
Cross country ski resorts. These areas charge a fee to use their groomed trail system.
Permit areas. Known in some states as Sno parks, these are areas where you can park for a fee in a plowed location close to trails and snow play areas.
Any area where you hike in the summer or ski off trail in the winter.
National forests and state parks.
Other mapped routes, established trails and controlled areas.