Don't forget Portishead's self-titled second album. People underrate it because it's not as magical as
Dummy, but it's no disappointment by any means.
"Humming" is a great song (with a great video),
http://youtube.com/watch?v=fzm1DY3hJL8
as is "Cowboys," which is badass live
http://youtube.com/watch?v=9HILtyPfMWk
Portishead claim to have another album on the way soon, but who knows.
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You mentioned Björk, and I never really thought of her as 'trip-hop,' but I guess one song of hers definitely is,
"Possibly Maybe"
http://www.youtube.com/watch?v=-Yrd0K9k-Gw