Rather unique style of bicycle pedal, brought to you by the wizards at Crank Brothers, that literally looks like an eggbeater. The geometry of the pedal provides four sides that the rider can "clip in" to while riding, and the eggbeater design allows the pedals to easily shed mud and other grime one might encounter. Eggbeaters were created primarily for mountain bike use (hence the mud-shedding), but they are becoming more and more common in the world of road cycling.
The original Eggbeater pedals were made out of stainless steel, and this model can still be bought today. However, coinciding with the aforementioned increasing use in road biking circles, other models are available that use lighter metals to cut down on those precious grams. The original steel design ends up being about 133 grams per pedal, whereas the newer "Triple Ti" model uses titanium components to bring the weight down to 92.5 grams per pedal. Of course, these lighter materials drive the cost of the pedals up dramatically - $140 for a pair of steel Eggbeaters, contrasted with $400 for the high-end Triple Ti.
Though more pricey than some other pedal systems, many cyclists find the Eggbeaters to be more convenient once they've gotten used to them. Unlike conventional road cycling pedals (which are two- or sometimes just one-sided), the Eggbeaters can be engaged without worrying about the orientation of the pedal. Basically, you can just put your foot down, assured that the cleat will engage with the pedal solidly. This is very handy in situations where you find yourself getting in and out of the pedals a lot - for example, mountain biking, or stop-and-go traffic on the streets.
The Eggbeater cleats are also unique in their design, relative to most traditional pedal systems. The cleats are reversible, allowing you to swap them between the left and right shoes depending on how easily you want to be able to engage/disengage with the pedal. This partly makes up for the lack of tension adjustment on the Eggbeaters themselves.
Finally, regardless of the metals used in a given model of Eggbeaters, the cleats themselves are made of brass. This allows the cleats to absorb most of the wear and tear of clipping in and unclipping, so that the pedals don't have to. The end result is you may have to replace your cleats somewhat more often, but this amounts to $20 or so every couple of years, at worst. Most cyclists seem to agree this is a reasonable amount to pay compared to the original cost of the pedals themselves. And relative to the generally exorbitant cost of high-end road/mountain cycling equipment, that's peanuts anyway.
More info about Eggbeaters and the other Crank Brothers products can be found at their web site: http://www.crankbrothers.com/