I also change at work, but, I prefer not to get wet (I also have a helmet cover, waterproof lobster gloves, and a good rain jacket). For a light mist I'll wear a pair of water resistant tights (though they're not really tight, so I just call them pants). I have waterproof rain pants for when it's really raining. I just buy the MEC house brand stuff.

I have all my rain stuff in a big zip-loc bag that always comes with me on the commute. A lot can happen in 8 hours at work, and this year the weather men seem to be worse than usual at predicting rain.