First is "Coyote," off Hejira. This song is pretty famous; Jaco Pastorious's bass playing is legendary. It also just conjures up a beautiful "western" image for me. Montana or Wyoming or (more likely) Alberta.
The second is "Don't Interrupt the Sorrow" from The Hissing of Summer Lawns.
What's interesting for me about Joni Mitchell is that while she's forever singing about either California or Canada (and occasionally Detroit), I truly got into her while living in Boston. And almost all her music puts me back in that city, usually on my bike, out on a weekend ride. This song places me back at a specific intersection in Cambridge, about a half-mile north of Harvard Square. It's got nothing to do with the song, but Joni Mitchell will be indelibly associated with Boston for the rest of my life. (So will Jackson Browne-- ironically another Californian, but the second I hear "Late for the Sky," I'm on a hill in Roxbury.)