There are several plugins that can prevent players from breaking blocks they are not supposed to. Below are some plugins that we have found to work well.
For Admin Use:
World Guard: This is a great plugin to help prevent players from damaging spawn areas. It has many options that also allow it to be used for a variety of other purposes. For more information on how to use this plugin, visit the World Guard Wiki.
For Player Use:
Grief Prevention: This is a plugin that allows players to claim a portion of land so that others cannot damage their builds or take items from their chests. For more information please visit the Grief Prevention Wiki.
Towny: This is an in-depth plugin that allows players to create towns and claim land on a chunk by chunk basis. There are many facets of this plugins and options for players to explore. For more information please visit the Towny Wiki.