How much stuff are you wanting to carry? You may not need a rack and pannier, you may simply need a good size handlebar bag and a rear bag. OR, since handlebar bags interfere with lights and you may need those commuting, you can get a good size rear bag such as this:
http://www.amazon.com/Topeak-MTX-Tru...ef=pd_sbs_sg22 But you will need the Topeak Explorer bike rack pictured on the same page just scan down a bit. It's also a good idea to get the yellow rain cover also pictured where the bike rack is.
PLEASE NOTE I don't think your bike comes with eyelets on both sides of the rear dropouts for bike racks, please check to make sure, if not that rack will not work.
If no eyelets then there's this option:
http://www.distancebiker.com/store/i...bags/q680.html It's a good size bag, expensive, but the biggest offered without needing a rack.
There are some racks that don't require eyelets, they fasten to the seat post and hang down so you can strap a pannier to it but if you should have something hit it from the side while moving it could shift the rail into the spokes then you got issues.
There is also just racks without the hanging rails but you cannot put panniers on which in your case is not a big deal. Performance and Nashbar sell these racks, they fasten to the seat post then you buy a bag that will fit that rack. Those racks are only good for about 25 pounds.
No matter which bag you get DO NOT expect them to be completely waterproof. You'll need to see if they sell a rain cover, and/or keep anything you don't want to get wet in ziplock plastic bag.