There is also the "MEL BAY'S COMPLETE IRISH TIN WHISTLE BOOK", ISBN 0-7866-2318-7. Or you can check out their site at http://www.melbay.com. (Sorry, but I don't know how to make the blue clicky thing.) I find the book quite instructive, with some basic music theory, explanation of different grace notes, lots of tunes, and fingering charts to make it easier if you're not a whiz at reading music.

Magpie