ObsidiPlates

Overview (Minecraft 1.4.7+)
ObsidiPlates is a mod, by Myrathi, providing pressure plates that can only be activated by players.

Originally created as a surprise for Jadedcat, it implements (using original code) a concept she missed from Better Than Wolves (which is why it uses obsidian, specifically).

Overview (Minecraft 1.5.1+)
As of Minecraft 1.5.1, Myrathi has added five more plates.

MossyPlates made with mossy cobblestone, that can only be activated by NPCs.

SilentPlates made by crafting a ObsidiPlate or MossyPlate over a block of wool, disabling the clicking sound.

ShroudedPlates which can be added on to any previous Plate, can be crafted by alternating nether quartz and glowstone dust around the Plate, this makes them see through.

How It Works
All plates are a type of switch that can be placed onto a surface of a block. If connected by wire to an object (or placed adjacent to a block that can be powered), it will provide power to that object or block when stepped on by a player and will stop when stepped off.

As opposed to wooden and stone pressure plates, obsidian pressure plates will not respond to items or NPCs and mossy cobblestone plates will not respond to items or players.

Silent versions of these plates make no sound.

Shrouded versions of these plates are see through.

Silent shrouded plates can only be be crafted as silent first then adding shrouded last.

Recipe
ObsidiPlate

MossyPlate

SilentPlate

ShroudedPlate