A range of wireless camera kits all operating on the 2.4GHz frequency.
2.4GHz cameras have built in transmitters with 10mW output power. This strength transmitter will give you a maximum range of approximately 75m - clear line of sight. Obstructions will reduce this distance, metal obstructions (e.g. cars or wire mesh) will all but wipe it out. Indoors, you can realistically expect approximately 10m-20m.