Celtic Fantasy

[sleigh]

I'm putting together a literature class to study Celtic Fantasy. The mythic sources are pretty obvious, but I want the class to read a novel (or two) that is relatively modern and which dips into Celtic mythology. Yes, I know -- I could use my own Cloudmages series -- certainly HOLDER OF LIGHTNING would work -- but that would make me feel a little too weird and self-centered to require the class to read my own book, I think.

So what book(s) would you suggest? They have to be currently available and not out-of-print. What your favorite bit of Celtic Fantasy?