Lough, but pronounced "Luff."
It's a shame that's it's so hard to get their stuff in this country now. I've learned a huge number of great tunes from their albums, also of course from the Chieftans, including quite a number of airs, some already mentioned, others not. Although I learned many of them or even most for my fiddle, I usually learned them on whistle first. I have two notebooks pretty much full of tunes, including many beautiful airs, learned from their albums and others. (Incidentally, one of my shoulders is feeling so much better lately that I may have a go at playing the fiddle again.)
Another good place or two for some great airs are albums by Phil Cunningham and Aly Bain. The Pearl and The Ruby, for example. The title song, The Ruby, starts out exquisitely on whistle. Sounds to me like a Gen, enhanced a bit in the studio.
The first two Capercaille CD's also have some beautiful songs. They're all easy enough to learn by ear, but so satisfying to play.
(edited to add two more easy to learn airs)
Colsfield House -- I think that's on a Kevin Crawford album. Sounds really good on a Bb whistle. He plays it on flute, of course.
Caitlin Triall (Chieftan's Live). One of the first tunes I learned for fiddle, but it's nice on whistle, too.