If you're looking for a self-contained electric solution (which it sounds like you are), you may also want to look at the "counter electric dispenser" type setup also mentioned on the page that Glasseyed linked to.
Note, however, that this problem is actually a lot more complicated than it first seems, and likely has no "silver bullet" answer. The problem is that carbonation of beer is a tricky thing (a lot more so than for soda), and just getting it cold before it gets to the glass isn't necessarily good enough. As beer gets warmer, its capacity to hold CO2 decreases. This means that if your keg is not at the correct temperature, it will not have the right amount of carbonation. When you reduce the temperature, it increases the capacity for carbonation, but this isn't an instant process (it can take several days for carbonation levels to equalize inside a keg when force-carbonating it, for example). The end result is that even if you manage to chill it to the perfect temperature just before serving, you'll be serving perfectly-chilled flat beer.
Now, you might be able to compensate for this somewhat by keeping the kegs at a higher pressure, which will get the right keg carbonation level at the warmer temperature. The problem with this is then that you'll be dispensing with an unusually high CO2 pressure, which means the CO2 will come out of solution faster when it gets to an ambient-pressure environment (open air), which means foam.
You'd also need longer beer lines to account for the extra pressure so that the beer doesn't come out of the tap too fast (again, foam). Also, the longer the distance between the keg and the chiller, the less the effective pressure will be when your beer reaches the correct temperature, which means it may well already have lost some of its carbonation in the line and not have enough effective pressure to push more in even once it's cold enough to want to take it. Therefore, you probably want to mount your chiller as close to the keg as possible, up the keg pressure somewhat more than normal, and have long dispensing lines after the chiller (which is probably going to be an interesting balancing act), but this also means you've got a lot more cold beer in the lines that needs to be kept cold until it gets to the tap, so insulation/cooling of the long tap lines is critical as well.
Even if you manage to get all of that right, I suspect you may well end up with a setup where the carbonation level keeps changing depending on things like how frequently you're pouring from any particular keg, and may just end up varying back and forth between cold foam and cold flat beer..
(I'd love to be proven wrong, though, so if you do find a solution that works, please do share!)
