Hi !!!
Infrared transmission medium is good, but the range is limited to some 4feet (Max, I guess) and it's a bit troublesome to demodulate it. So I guess AM should be good and easy. Both to transmit and receive. As 'Jeff corr' said, use 555 but instead of glowing an IR LED connect it to a telescopic antenna , For more power (in case of larger range and noise immunity) transmit it at high power using some HF transistor (which will be as a switch).
..and for receiver connect an antenna , (use a preamplifier, if needed) and then pass the signal through a Detector diode (4148), and a Low pass filter .. U'll get the modulated signal. If needed pass it through a 7414 . I guess It'll work. U'll need two of these ..and both transmitter at different freq. Take a dipole antenna of length ¼, 1/6 or 1/8 wave length, and U'll have omni direction radiation pattern in horizontal plane. Use the freq range of 2Mhz to 20Mhz . Well this freq spectrum should be free of most commercial AM freq. ..and I hope the transmitter output wont interfere with the clock or other signal on the controller.
If you transmit "10101010 "
+v
Transmitter output: |||||__|||||__|||||__|||||__0v
+v
At receiver antenna: |||||__|||||__|||||__|||||__0v
||||| ||||| ||||| ||||| -v

after diode and low pass capacitor: """__"""__"""__"""__0v

Regards
Vignesh Baliga