Two options which I have experience with are the Banjo Brothers Backpack Pannier and the Arkel Bug. The Banjo Brothers bag is great for the cost, but the design is not the best for people who like lots of storage options to keep things organized. I replace my Banjo Brothers bag after about a year and a half of use when I decided to upgrade to the Arkel. The Arkel Bug is an awesome pack that can hold my bottles, lights, helmet, gloves, and everything when I get off the bike at the end of my commute. The only thing I don't like about the Arkel is that the bag itself is not waterproof, so the pack cover, and a pack liner for really wet and flooded days, is necessary to get with the bag.

I agree that the list posted by BikeLite is a great place to start looking at features and budget.