You are absolutely right. There is always something more to learn, no matter how experienced you become. I am always scouting the internet and browsing the book stores for new learning resources.
My top recommendation right now would be to look out for Hugh Lawtons books on digital photography. Three wonderfully written volumes that have transformed the way I work and taught me more than I ever could have hoped for.
Photography in the Digital Age (http://www.manzanita-ent.com).