Nordic Semiconductor nRF2401A. Transceiver chip operating in the 2.4GHz band. This is a truly spectacular chip with all sorts of possibilities.
  - New silicon revision - not only less expensive, but more sensitive (-93dBm)
  - Software selectable channel from 2400MHz to 2525MHz (125 Selectable channels)
  - Minimum number of external components
  - Lots of application notes and support on Nordic Semiconductor Website
  - Works very well with the 16MHz SMD Crystal