Best first track

Rolling Stones "Miss You" on "Some Girls."

More, and less conventional listings:

Tonio K- Life in the Food Chain-Life in the Food Chain

PJ Harvey- Rid of Me- Rid of Me

Patti Smith - Horses -Gloria

Bright Eyes: "At the Bottom of Everything" from "I'm Awake, It's Morning."

Marvin Gaye:  "What's Going On." from album of the same name.

Couple more:

John-Madman Across the Water: Tiny Dancer

Johnny Nash-I Can See Clearly Now: I Can See Clearly Now

A  few more:

Dylan "Free Wheelin'" -- "Blowing in the Wind"

Dylan "Blonde on Blonde" -- "Rainy Day Woman"

AC/DC "Back in Black" -- "Hell's Bells"

Jazz has plenty of examples:

Rollins-Saxophone Colossus: "St. Thomas"

Coleman-Shape of Jazz to Come: "Lonely Woman"

Coltrane-Love Supreme: "Part 1"

Brahem, Anour-Thimar: "Badra"

For classical, it is hard to pick favorite opening movements or single movement works, but the following come to mind:

Shostakovich-Piano Trio No. 2

Beethoven-Violin and Piano Sonata No. 5 ("Spring")

Mozart-Vesperae Solennes Confessore

Adams-Violin Concerto