The usual wealth of information available at Erowid. Chemical structure, numerous FAQs, Law, Articles and Trip Reports are all there. Almost no need to go anywhere else for info relating to acid.
A rather long article on LSD from Wikipedia. Contains information on dosage, effects, history, legal status and some very interesting stuff in the 'Urban Legends' section. A great read.
Albert Hofmann discovered LSD in the 1950s. This is his book on the topic - online.
A very practical guide to LSD, its dosage, its effects, addiction, tolerance and legality. Contains a great 'Mixing with other drugs' section.
Everything you ever wanted to know about magic mushrooms can be found on this site. Topics range from first trips to cultivating your own. The full list of topics would probably take up the rest of this page. A must see.
A great article on mescaline, which is a psychedelic that is widely used in Native-American religious rituals. Be sure to expound on the article by checking out the links on the bottom.
A site that contains plenty of info on Salvia Divinorum. It is a plant with a strong psychedelic potential. Not many people know about it, hence it is legal and available for purchase over the net. The trips last just a few minutes, but can be stronger than LSD.
DMT is one of the strongest psychedelics and it gained fame after it was popularized by Terence McKenna. Erowid contains a wealth of information on this substance, enough to keep you reading about DMT for hours.
A resource dedicated to ayahuasca - a powerfully psychedelic brew of South American DMT-containing plants. It is used spiritually and therapeutically in the South American shamanistic tradition.