Minecraft X-RAY Xray X-ray Base Class Free, Forge+Liteloader
Latest version available at: ☞ http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/1287646--
This mod requires Liteloader.
To install this mod, just drag it into the mods folder, located in your %APPDATA%/.minecraft folder on Windows.
Uyjulian's X-RAY Mod will let you see through any Block in Minecraft. You can choose any block to be visible or invisible. This mod has ONE control.