School Bands and Marching Bands
Band Geek Love by Josie Bloss (YA)
Sequel: Band Geeked Out by Josie Bloss (YA)
Audition & Subtraction by Amy Fellner Dominy (MG)
Major Crush by Jennifer Echols (YA)
Julia Gillian series by Alison McGhee, illustrated by Drazen Kozjan (MG)
Deep in the Heart of High School by Veronica Goldbach (YA)
Good Enough by Paula Yoo
Rock Bands and Musicians
Knights of the Lunch Table #3: The Battling Bands by Frank Cammuso (MG)
The Disenchantments by Nina LaCour (YA)
So Punk Rock (and Other Ways to Disappoint Your Mother) by Micol Ostow with art by David Ostow (YA)
Rock On: A Story of Guitars, Gigs, Girls, and a Brother (Not Necessarily in That Order) by Denise Vega (YA)
The Last Days by Scott Westerfeld (YA)
Also of note:
If I Stay by Gayle Forman and the sequel, Where She Went, because Mia plays the cello and Adam is in a rock band. (YA)
And for the picture book crowd: Emmet Otter's Jug Band Christmas by Russell Hoban. Read this, then watch the movie adaptation. It doesn't matter what time of year it is. Just watch it.
Related booklists at Bildungsroman:
But I Don't Want to Be Famous!
But I DO Want to Be Famous!
Sing Sing Sing