Any writer is nothing without resources. Sure, we have our imaginations, but that's not enough. I've shared some of my favorite go-to sites for research before. Here are some I missed (in no particular order).
Nami.org - The National Alliance on Mental Illness houses the most extensive information on all facets of mental health.
AnimalPlanet.com - Animal Planet's site features information on all kinds of animals - domestic to feral to wild. Its coolest feature includes a dog and cat breed selector. This is great if you want to add a pet to your story and the pet needs certain characteristics.
Fabrics - Need to know the difference between nylon and rayon? You will if your villain is caught in a burning building. If you want him to really suffer, he should be wearing a nylon jacket (it melts before it burns).
Collegeboard.org - The College Board site offers everything you need to know about colleges around the world. Where is someone most likely to attend if they are premed? Which are the best small colleges? Find out how your young protagonist can get help to pay for college.
AutoTrader.com - Need car facts? Is one of your characters selling an old Buick? This site will give you a suggested price for buying or selling almost any car.
National Institute on Alcohol Abuse and Alcoholism - Just about everything you need to know about alcohol and its effects on your body and you. Check out the facts about underage drinking for your YA characters.
Not everything you read on the Internet can be trusted. I look for familiar sites or those run by nonprofits or the government. I try to avoid sites that are selling something or that you have to register with before you get your info.
Here's an article from the University of California that you might find helpful.
Keep up the great research!