An excellent resource dedicated to healthy vegan diets is Veganhealth.org maintained by Registered Dietitian Jack Norris. I have a laminated copy of his daily recommendations for vegans posted front and centre on my refrigerator and it keeps me on track. Just about anything you need to know regarding plant based nutrition can be found there including information about supplements, meal plans, nutrients that need special attention, vegan kids, food allergies and the latest research on plant based diets. There are numerous articles on many more topics that are easy for the lay person to understand. I highly recommend this site.
When I first considered transitioning to a completely plant based diet, I was lucky enough to have made the acquaintance of Ginny Messina who is a highly respected vegan dietitian and the author of several books on nutrition. Without her invaluable advice I would have felt much more nervous about the journey I was about to embark upon. Ginny writes excellent regular articles for the Examiner.com online summarizing and analyzing the latest scientific research in nutrition and other topics related to veganism. You can read and subscribe to her articles here. She also maintains a website/blog called The Vegan R.D. with clearly written information, a vegan food guide and links for anyone interested in vegan nutrition.
The Vegetarian Resource Group is an extensive website with articles, recipes, food ingredient information, a restaurant guide and much more. They have various publications, guides and books available, some for free and some for sale. Articles and information in Spanish are also available.