When we saw these Fragpedal USB Gaming Footpedals back at E3 2006 buried in Kentia Hall, we thought the concept was interesting, but reserved judgment until we could get our feet on them. i4u just got a pair and they seem to really like them.
The Fragpedals are essentially four buttons that you hit with your feet that you can map macros to. It's useful when you map functions that are either inconvenient to hit with your keyboard or ones that you want to hit simultaneously with your keyboard. The pedals themselves are rubber-backed and non-skid, so they usually won't slip around when you're gaming. The price of $69.95 isn't too cheap, but it's not exorbitant either if you do a lot of gaming.
In games like Command and Conquer, he was able to map keys and step on the pedals to activate them easily so he wouldn't have to move the mouse away from whatever it was he was doing.
One quirk the i4u guys ran into was that there's no tactile feedback when you're using it. So if you're typing away on chat and get a bunch of random keys showing up, you probably have your foot on the pedals.