What are some challenging acoustic songs out there that I can play?

I've been playing Andy McKee's "Drifting" here: http://www.youtube.com/watch?v=Ddn4MGaS3N4

And it was challenging, but all you need is practice and coordination to play that song.
I was wondering what other acoustic songs that seem challenging at first, but are able to get it down with practice?
Appreciate Music.