Song playing in Kanon (2006) episode 8
That song is called "Yume no Ato", which means "After the Dream". It's Track 2 of the Kanon original soundtrack, which I was pleasantly surprised to find can be purchased on iTunes, along with lots of other great anime music (including the OSTs for Clannad, Little Busters, Charlotte, Angel Beats, Planetarian, and Rewrite).