General Tinwhistle

Ricci Adams' Go here if you don't know anything about reading sheet music, but want to learn. Excellent resource!
Chiff and Fipple (be sure and check out the message board!)
Brother Steve's Tinwhistle Page   A great, free learning resource.
Michael Eskin's TradLessons on YouTube  Another free resource, with close-up videos of the whistle action.

Sheet Music & Tablature

Henrik Norbeck's Abc Tunes
The Session
JC's ABC tune finder- (TONS of tunes)
Richard Robinsons Tunebook
Traditional Irish folk music tune-book
Tunes at Ceolas
MakeMusic I use their software, Finale, to make the sheet music for the site.

Lyrics Resources

The Mudcat Cafe

Recordings and Session tunes

Tin Whistle Tunes--recordings of everyday folk playing the whistle

Music Shops that Sell Whistles

These links lead to most of the vendors I've dealt with buying whistles over the years. These are big music shops, like Hobgoblin, Lark in the Morning, etc. I'm not linking to individual whistlesmiths , such as Paul Busman, Copeland Woodwinds, etc. That's because there are something like a fifty or more whistlesmiths making whistles now, and that's a lot of links to make you wade through. If you want to find an individual whistlesmith's website, please check out my reviews, as all of my reviews have a list of websites where you can get the whistle in question. if you're still having trouble, or I haven't reviewed that make of whistle yet, feel free to send me an email! These links are by no means the complete list of whistle shops out there!

Lark in the Morning -- They have everything, ask for a catalog. It's way cool.
Melody Music -- In my hometown of Houston. Also, the only place I've been able to easily get mail order Duponol from.
Elderly Instruments
The Irish Flute Store
Hobgoblin Music
Whistle and Drum