Raise you're hand if you've actually used a ring light and not one that uses LEDs and is made for macro.
You can get an ABR800 for $399. That's a 320 w/s ring light with modifiers that control how hard/soft the light is. If anyone's ever shot a person with a ring light, you'll notice this cool little effect where the catch light in the eyes are little white circles which are reflections of the flash tube. They're not red dots like say a flash that is bouncing right from the subjects eyes and into the lens.
Also, if you go on the some what general consensus that most speed lights are about equivalent to 60w/s, with the pop up flash being about 15 iirc, then the ABR is has about five times as powerful. It also has a recycle rate of 1 second, so it's going to smoke a speed light that takes 4-7 seconds.
The down side? Battery pack. But there are modifiers that attach to the a speed light and act just like a ring light. You lose power, but if you're shooting with a 580EX II or an SB900, then you may have a little bit to spare. They're expensive, running $150-$300 for the two that are actual products and not homemade. That would probably be the best bet as you can use it, then remove it.
There is a member on one of the forums I frequent that uses an ABR800 for event photography. He bought the vagabond and fixed it so he can carry it in a back pack. I think it's rated at about 1200 shots at full power with a B800, so there should be no difference in power comsumption. I'm sure it's a bit heavy, but hey, he has enough power to destroy anyone else in the room that's not shooting with monolights or anything similar.
http://alienbees.com/abr800.html
http://strobist.blogspot.com/2008/03/full-review-ray-flash-ring-flash.html