The most comprehensive listing of mycological resources on the internet is The World-Wide Web Virtual Library: Mycology, with scores of links of interest to professionals and amateurs.
Don't miss Ari Kornfeld's Natural Perspective, an excellent tour of the natural world. Natural perspective has lots of information on the Fungus Kingdom.
Interested in the phylogenetic relationships of living organisms? Then go to the Tree of Life project. This massive work in progress has information on all organisms, including the Fungi.
A fine page, mycoElectronica, has articles on mushroom stamps, mushroom poisons, and back issues of "The Puffball", the official newsletter of the Willamette Valley Mushroom Society located in Salem, Oregon.
If you have ever collected there, you know that the Pacific Northwest is Mushroom Heaven. This is a nice page with good information.
From Slovenia is the very well done Wild Mushrooms: How to Find, Cook, and Eat Them -- and Survive! Photos and descriptions of "the good, the bad, and the ugly".
At Ralph Czerepinski's Finest Fungi Fancier File there is information on mushroom eating safety rules, reviews of mushroom books, and information on favorite edible mushrooms.
From Italy, Mycopage has beautiful photos along with English abstacts of articles from Italian mycological journals.
You can read the Snohomish County (Washington) Mycological Society's newsletter at Igor's Home. You can also see a picture of Igor with his 'morel cap'!
There is very good information about mushroom poisoning and mushroom toxins published by the Food and Drug Administration. The information is a chapter from Foodborne Pathogenic Microorganisms and Natural Toxins 1992.
Visit Tom Volk's Fungi for information on the taxonomy of Armillaria, including a key, and lots of photos of fungi.
Although they are not really fungi, the slime molds (myxomycetes) have traditionally been studied by mycologists. And they are fascinating organisms. For information visit The Internet Guide to Myxomycetes.
The NHBS BookNet is a mail order bookstore with a searchable database of over 40,000 in-print or forthcoming books, videos, cassettes, CDs, & CD-ROMs on natural history subjects. Thousands of books on botanical subjects and a search on 'mycology' yealds a couple hundred hits!