I'm an Arkel man myself, but for the money I have found Banjo Brothers gear to be a great value.

http://www.banjobrothers.com/products/panniers.php

I have not used their panniers though and I'm not sure whether they have some type of mechanism that locks them on the rack rail like Arkel and Ortlieb. Frankly, I am wary of panniers that do not lock on since I have had less than satisfactory results with others.