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.
Canadian ADHD resource Alliance Resources for both professionals and patients, including treatment guidelines,
Centre for ADHD Awareness, Canada Site for ADHD information and advocacy
National Attention Deficit Disorder Association
Children and Adults with ADHD, CHADD
National Resource Center on AD/HD