Too bad Panettiere's "Yellin' From The Rooftop" isn't on the first soundtrack (or the second), but still. "For Your Glory" is also wonderful, as are "Consider Me," "I'm A Girl," "Boys And Buses," "Telescope"...
Bowen and Sam Palladio's duet on "If I Didn't Know Better" from the pilot is a heartbreaker, and Bowen solo doing "Twist Of Barbwire" kills Jonathan Jackson's take on the same song. How can you go wrong sounding like Nanci Griffith? You can't.
All the above songs are included on the four-disc set The Music Of Nashville, Season 1: The Complete Collection (which isn't quite complete, as there are still a few songs completely unreleased).
Lennon and Maisy Stella with "Telescope" and "Ho Hey" are universally considered show highlights.
Most of the duets seem to qualify, such as Scarlett and Gunnar's in the pilot and Juliette and Rayna's "Wrong Song". Solo numbers hit the target as well, such as Juliette's two songs in "I've Been Down That Road Before" and her performance at the Bluebird in the season one finale.
That Clare Bowen is the first cast member to have an iTunes album solely devoted to her is pretty impressive in itself (though Hayden Panettiere became the second a week later).