There are lots of resources available online for learning or improving your whistle or ITM playing.
First, and probably the best, is the forum on the Chiff & Fipple website. There is tons of information available there on every conceivable subject, and if you don't see what you're interested in just ask; the participants of that forum are some of the most knowledgeable people in the world on ITM in general, and whistle playing in particular.
Also, check out our links page, our glossary (of common ITM and/or whistle terminology) and our getting started page.
Then let us know if you'd like to see something else here on the Irish Whistle Shop website, we're here to serve you!
the Irish Whistle Shop