For my lighweight commuter I really didn't need that big of a pannier system. I decided to go with the Topeak RX expandable trunk. I have never really filled it yet but it does not hold a ton of gear. I usually commute with spare tube, lunch, levers, commuter pass, wallet, ipod for train, cell phone, cliff bar, fresh work shirt, shorts for the after noon ride home, etc.. It's the perfect size for my needs. Whats really nice about this bag is that inside there is a shoulder strap so once at work with a single button I can slide the pack out of the dovetail connection on the rack and sling the bag over my shoulder like a "MAN PURSE" or use the handle instead of the sling.