anything by the following artists always inspires me:

andy mckee
paul gilbert (acoustic samurai album)
rodrigo y gabriela
micheal hedges
don ross

Emerson, Lake & Palmer has some great acoustic stuff.

So does Pink Floyd.

Beatles translates well, but so does Led Zeppelin.

(Must be easy to tell I'm an old fart.)

well all of the above people plus.....HIM. i bought one of their albums which is all acoustic. its really good.

I know this probably helps no one, but there is a song that a guy my mom went to high school with wrote; she used to play it for me when I was growing up, and it is a beautiful song. If I can get my video back up I'll get my mom to play it and I'll post it so everyone can see. It's good stuff...trust me....

My top 3 :)

Desiderata by Greg Howe
Dust in the Wind by Kansas
Classical Gas by John Williams

When I think of a good song, I tend to think of 3 things:

1) Emotional content! It has to be able to move me on a level that other music just can't seem to do.

2) Melody! A good key to making #1 happen is a good melody.

3) Harmony! A good harmonic structure underneath the melody is key to helping enhance and build upon that emotional content.

So, that being said, the #1 acoustic song for me is:
Desperado - Eagles