[U]Rush-YYZ[/U] (Instrumental) Every instrument stands out in this song, not just guitar.

[U]Jimi Hendrix: Little Wing[/U]

[U]Pink Floyd: Shine On You Crazy Diamond[/U] (All in all, it's about 23 minutes long though, not a lot of vocals, but a little)

And Like Blues-man said, Voodoo Child would be a good choice.