I'm well along on an infrared transmitter and receiver, using an AVR '2313 chip. I wonder if there is much interest in this here - perhaps more in the home automation boards. Here's a summary
Receives infrared signals from common TV/audio remotes.
Sends the details of the timing of every bit transmitted to a PC or other device via a serial RS232 connection at 19.2Kbaud.
The PC or other device can send the same information which it received out the serial RS232 to the AVR chip and my program will emit IR of the same timing, to control a device.
Hardware: Olimex (or equivalent) AVR protoboard ($15?). a '2313 or equivalent chip. IR receiver chip ($4), from Radio Shack, Digikey, others. IR diode or emitter from some IR device like an IR blaster.
My AVR code. Visual Basic demo/test program.
I developed this having found no such AVR based thing on the net. There are lots of receivers, but no bi-directional things.