I'll toss a few of the things I have labelled as 'Instrumental' on my mp3 player. A few of these aren't... really instrumental, but I guess my definition includes "I don't know what the righteous fuck they are saying but it sounds pretty."

[youtube]https://www.youtube.com/watch?v=Bij6d-KU4aA[/youtube]

[youtube]https://www.youtube.com/watch?v=K1ryJDVuZ6k[/youtube]

[youtube]https://www.youtube.com/watch?v=xERitvFYpAk[/youtube]

[youtube]https://www.youtube.com/watch?v=IJiHDmyhE1A[/youtube]

[youtube]https://www.youtube.com/watch?v=wlPtmws131o[/youtube]

None of these are really long... because I don't have really long songs on my mp3 player. That'd get annoying. Off the top of my head, the only long-ass music that might not be an obvious choice is the [url=https://www.youtube.com/watch?v=Isic2Z2e2xs]Planet's Suite[/url].