Sierra Designs recently introduced a unique rainwear option: a very long jacket paired with a pair of chaps. See it here:
http://www.sierradesigns.com/product/elite-cagoule. The fabric itself is not breathable, but the garments are designed to allow a lot of airflow. Total weight of jacket and chaps is only 11.5 oz. I've seen a couple of favorable reviews. I'm interested in comments from anyone who has tried these products.