I just ran across this amazing posting on veganbaking.net. To replace one egg, I always use the 1 tablespoon ground flax seed to 3 tablespoons warm water formula. I’ve never really got into the science of why it works, I just know it does, but this article is amazingly detailed and informative.
http://www.veganbaking.net/recipes/egg-replacers/flax-seed-egg-replacer