This is quite possibly the most simple trap but it does require a lot of resources as it requires
TNT: http://www.minecraftwiki.net/wiki/Tnt and stone pressure plate: http://www.minecraftwiki.net/wiki/Stone_Pressure_Plate
first you dig a hole any where that is at least 3 blocks away from your base then place a block of TNT in the hole and on top of it place a pressure plate. when stepped on it will trigger an explosion you may wish to place it above a two block deep hole when placing it on top with a gap between it when stepped on it will gain gravity leaving the victim in a hole which reduces the distance between him/her and the trap. this trap however is easily set off and any animal can set it off and it is devestating and can destroy your base.
above is a picture of the land mine
