These can be used for more than writing fantasy, but fantasy is what I do, and my list of links is tailored to what has helped me.
The Art of Travel – This site, actually the text of a nineteenth-century book, describes the process of traveling in wild areas. It describes methods of travel that can easily be adapted for different eras and circumstances.
Behind the Name – This easy-to-use database of first names and their meanings is great for naming characters.
International Colored Gemstone Association – In fantasy, somehow, gems tend to come up. (Maybe that’s why they call it “fantasy”?) This site helps choose the right rock for the job.
The Language Construction Kit – If you’re creating a new language – well, congratulations on being hardcore. This site has some great tips and things to think about.
AgentQuery – Provides information about numerous literary agents.
James River Writers – This is a great group, especially if you live around Richmond, VA. Even if you’re not local, it’s worth checking out for the annual conference alone.
Society of Children’s Book Writers and Illustrators – A fun and useful organization to belong to, with critique groups, contests, and more.