Can someone recommend a few Joni Michell albums?

For the Roses, Hejira and, of course, Blue.

"Hissing of Summer Lawns", "Don Juan's Reckless Daughter", and "Court and Spark". "Miles of Aisles" (a live album that is essentially an overview of her earlier work). I recommend them all very highly.
She also made an appearance on a Herbie Hancock album called "Gershwin's World" which is beautiful and revelatory for the stark way it illustrates the changes to her voice and style that have happened since "For the Roses."

Blue is indeed widely regarded as her classic album.
It's available as a HDCD disc on the most recent remaster.
It's pretty much straight ahead Joni songwriter style with acoustic guitar and piano prominent.
It's reflective in mood and was apparently influential on Dylan prior to Blood On The Tracks............