I have found that inexpensive panniers can be quite adequate. If money is no object go ahead and buy some Ortleibs. If the budget is tight I found both the Nashbar Waterproof panniers (Performance has a similar one) and the TransIt Pro Panniers (Performance) to be a great value. If you watch the sales and watch the coupon forum you might be able to get all 4 panniers for as little as $50 for the whole set!

Three of us used some combination of these models for the TransAmerica (4,244 miles, 73 days) this Summer and are quite satisfied with them. They worked well and are quite durable. I would definitely buy them again if I needed to replace them for some reason, but I am sure they have many thousands of miles left in them so that isn't necessary.