Monster Spawn Highlighter Mod 1.7.10. The name basically says it all. The mod will highlight any blocks where monsters can spawn.
Screenshots:
How to install Monster Spawn Highlighter Mod 1.7.10
Download links for Monster Spawn Highlighter Mod 1.7.10
Other Versions:
For Minecraft 1.5.1
Forge: https://minecraftlucky.com/dowload/file-6677
Mod Loader: https://minecraftlucky.com/dowload/file-6678
For Minecraft 1.4.7
Forge: https://minecraftlucky.com/dowload/file-6679
Mod Loader: https://minecraftlucky.com/dowload/file-6680
For Minecraft 1.5.2
Forge: https://minecraftlucky.com/dowload/file-6681
Mod Loader: https://minecraftlucky.com/dowload/file-6682
For Minecraft 1.6.2
Forge: https://minecraftlucky.com/dowload/file-6683
Mod Loader: https://minecraftlucky.com/dowload/file-6684
For Minecraft 1.6.4
Forge: https://minecraftlucky.com/dowload/file-6685
Mod Loader: https://minecraftlucky.com/dowload/file-6686
For Minecraft 1.7.2
For Minecraft 1.7.10