I shoot with the EX1 daily outside and have been using the Porta Brace Rain slicker. I like it alot, it's well designed and has good access to all the buttons on the camera. Plus the Cover for the lcd provides nice shade for viewing.
I always carry a thick clear plastic tarp folded in my camera bag just in case it starts to down pour and I'm out in the field... It's virtually free and will save you in a pinch. Obviously not for use when you know it's going to rain, but a great way to save your camera when the weather turns sour.
Also, Cinebags makes a backpack that I've used, it has a rain cover that goes over the whole bag... I can fit my EX1, zacuto rails and FF, Letus Extreme and about 5 primes in there too, along with my laptop and hard drives and a few other goodies. Just a thought.