Here are some protection plugins I found for you… might not be all of them, just did a quick search on the forums.
Current Sponge Protection Plugins:
FoxGuard (Similar to WorldGuard, made by @gravityfox) can be viewed here.
Polis (Not mainly a protection plugin, but has some features that allow for it) can be viewed here.
ExplosionGuard (Not a complete protection plugin but to my understanding can protect from Explosions) can be viewed here.