Planetminecraft.com provides a list of monster spawner IDs for Minecraft. Monster spawners are special blocks that are mined using a pickaxe. These blocks become active when a player character is standing within a 16-block radius of the spawner, and they cause monsters to appear nearby.
A monster spawner block is capable of spawning monsters in mid-air, bypassing normal spawning rules to do so. However, the spawner does not cause a monster to appear if the surrounding environment type is not suitable for that variety of monster. To use a monster spawner, players type "/give" followed by the ID of the monster they wish to spawn.