Any web search on Irish folklore, mythology, or fairytales yields a ridiculous number of hits, and wading through them can be daunting. Most are parts of personal web pages, and many are visually attractive and fun to visit, but do not give much relevant information. The sites listed below have been selected for their breadth of scope, and because they make good cases for the authority of the information they present.
British Council Poland: British Studies Web Pages: Articles on Irish myth.
[http://elt.britcoun.org.pl/m_celts.htm]
Provides synopses of and links to two articles on Irish myths and legends. Both articles are well-written critical essays by reputable scholars. The British Council is "an international organization for educational and cultural relations." It is registered in England as a charity.
Irish literature, mythology, folklore and drama. Anniina Jokinen's Luminarium.
"Created by Anniina Jokinen on March 14, 1996. Reinstated on October 8, 1996. Last updated July 24, 2000."
[http://www.luminarium.org/mythology/ireland/]
This is a one-stop shop. It contains dozens of links to very good pages about Irish myths, folklore, history, etc. All of the link pages provide source information, and the Luminarium homepage claims that all pages included on the site are "verified from authorized material." The Luminarium seems to be an informal e-library of certain humanities subjects; it is not affiliated with any university and is non-profit, but many of the listed contributors are either students or professors of national universities.
Searc's Webguide to Irish Mythology.Copyright 1997-2000.
[http://www.searcs-web.com/myth.html]
Another good introductory page; it has many links to tales, provides a link for a chronology of Irish myth, and only includes pages which provide source authority. There are also links to published essays, and even a PhD dissertation on a pagan goddess/fairy!