The RF remote is the power remote for "Front Row", the Mac entertainment center.  Unlike the regular infrared remote that ships with the Mac, this one doesn't require a line of sight and will even work through walls, furniture and from the  bathroom, as long as you are in the 60 feet range.

The remote control features a 9 buttons to control Front Row, adjust volume, eject DVD/CD and wake up or put the Mac to sleep. Oh, yes it also works with other apps if you a bit of tweaking. Available for US$ 30.99 from Amazon