best vocal harmonies in rock

Lyle Lovett/Rickie Lee Jones on Joshua..., Both Trio Albums: Ronstadt/Parton/Harris, Bruce Cockburn/Lucinda Williams (Isn't That What Friends Are For?), the Streisand/Gibbs album, Mark Knopfler/Emmylou Harris (at times), Linda Ronstadt/Aaron Neville, K.D. Lang/Martino. Admittedly, none of these are long term pairings but the work they occasionally did together was wonderful.

Just some off the wall suggestions to add to the superb obvious choices already given.

Dixie Chicks (suggested by my wife). Are any of you familiar with the accapella group "The Bobs" (of which no member is really named Bob)? They are very funny at times, quite amazing and will drive you nuts after too many plays in a row.