The following is a short list of reputable web sites that provide some solid information on ADHD. That is not to say that I would agree with all of what you will find posted on these sites. Nevertheless, they generally provide information based on solid clinical experience or research and are not trying to sell snake oil or fear mongering.
Totally ADD Provides tons of useful information with a sense of humour, and a lot of great video content.
Canadian ADHD resource Alliance Resources for both professionals and patients, including treatment guidelines,
Centre for ADHD Awareness, Canada Site for ADHD information and advocacy
Diet and Weight Management Strategies for Adults with ADD (ADHD)By Kathleen G. Nadeau, Ph.D