I just put an MSD off-road coil in my truck, and seems to have made a world of difference in performance. The coil itself is much more powerful than the OEM one, and it's filled with epoxy instead of oil, so it doesn't come unwound under rough conditions (hence the reason why it's called an off-road coil).
As far as actual performance increases, I don't have access to a dyno, but it sounds like it's running significantly stronger, and its acceleration has improved a good bit.
More information is here:
http://www.msdignition.com/coil_blaster_3_8222.htm
