Hey

What about a shield with one or more:
- infrared LEDs
- sensors operating on the same frequency / range? 

The idea is that these little shield modules could talk to each other over distance (line of sight) using the equivalent of Morse code or whatever the programmer decides. 
( Also, you could have your shield change channels for you on your TV.    )

A TV-Be-Gone shield would be awesome!

You post it before me. good idea

gets my vote

I'll fourth it. Sounds great.

This could be cool.  If there ends up being LEDs and IR sensors on this, it would be really nice if there was an option to not have the LEDs so someone could solder in a jack to connect an IR transmitter that's on a cable, and the same for a IR sensor.  One of these in combination with blue tooth or a wifi shield could be really fun to play with... or it'd be awesome to integrate it with something like openremote.

This definitely gets my vote.

[IrDA2 click Schematic:]

mikroElektronika produces the IrDA2 click which could be made into a TinyDuino shield.
IrDA2 click Schematic: http://www.libstock.com/img/projects/21707/372/1341389558_irda2_sc.jpg
It uses
MicroChip MCP2120 Infrared Encoder/Decoder at 6.0 x 8.65 x1.25 mm is $1.16 individual cost, $0.80 for 100  (Mouser)
Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/21618b.pdf
Vishay TFDU4101 infrared transceiver module at 9.9 x 4.2 x 4.7(with Domes) mm is $5.19 individual cost, $3.89 for 100 (Element14/Newark)
Datasheet: http://www.vishay.com/docs/81288/tfdu4101.pdf
7.3728MHz Crystal at 5.2 x 7.2 x 1.3 mm is $0.87 individual cost, $0.64 for 100 (Digi-Key)
Datasheet: http://www.mouser.com/ds/2/3/ABMM-40073.pdf

Also an interesting project "IrDA Enabling a PC or Microcontroller" shows a PSP talking IrDA protocol to an Arduino through the IR link using a Vishay TFDU4300 (The Vishay TFDU4300 is obsolete but I think a TFDU4301 should work fine in its place). Interrupts are implemented so that the Arduino can do other stuff while waiting for IrDA communication. This could also be used as a template for creating a TinyDuino shield. I think the supplied Arduino code in the article should work but may need some tweaking of baud rate and timeout length.

Alternate IR Modules
Vishay TFDU4301 infrared transceiver module is $5.35 individual cost, $4.37 for 100 (Element14/Newark)
TFDU4301 datasheet: http://www.vishay.com/docs/81965/tfdu4301.pdf

Here is a great resource on IrDA: http://www.societyofrobots.com/electronics_irda_tutorial.shtml