You may know many of these songs, or you may not. While they don't represent my fifty favorites - I don't think it's possible to construct that list - I've found them all consistently interesting:

Animal Collective - Fireworks
Animal Collective - Brother Sport
The Arcade Fire - Neighborhood #2 (Laïka)
The Beach Boys - All I Wanna Do
The Beatles - Hello Goodbye
Belle & Sebastian - Get Me Away from Here, I'm Dying
Belle & Sebastian - Put the Book Back on the Shelf
Bob Dylan - Like a Rolling Stone
The Byrds - Mr. Tambourine Man
Chris Bell - Look Up
The Danielson Familie - Did I Step on Your Trumpet?
The Flaming Lips - When You Smile
Grizzly Bear - Two Weeks
Hem - Half Acre
Hüsker Dü - Terms of Psychic Warfare
Iron & Wine - The Trapeze Swinger
Jackson Browne - Running on Empty
Jellyfish - The Ghost at Number One
Mates of State - I Have Space
Magnetic Fields - 100,000 Fireflies
Man Man - Gold Teeth
Mercury Rev - Downs Are Feminine Balloons
Modest Mouse - Gravity Rides Everything
My Bloody Valentine - When You Sleep
Patti Smith - Kimberly
Pavement - Trigger Cut/Wounded-Kite at :17
Pink Floyd - Time
The Pixies - River Euphrates
Procol Harum - A Whiter Shade of Pale
R.E.M. - Harborcoat
The Replacements - I Will Dare
The Rooks - Drag of the Month
Saturday Looks Good to Me - Bright Green Gloves
Saturday Looks Good to Me - Meet Me by the Water
The Shins - Saint Simon
The Shoes - Not Me
Simon & Garfunkel - The Only Living Boy in New York
Simon & Garfunkel - The Sound of Silence
Sufjan Stevens - The Predatory Wasp of the Palisades Is Out to Get Us!
Sufjan Stevens - Vesuvius
Talking Heads - This Must Be the Place (Naïve Melody)
U2 - Where the Streets Have No Name
The Vaselines - Son of a Gun
The Walkmen - Rue the Day
The Walkmen - Thinking of a Dream I Had
Wilco - Hotel Arizona
Yo La Tengo - Five-Cornered Drone (Crispy Duck)
Yo La Tengo - I Heard You Looking
Yo La Tengo - Nowhere Near
The Zombies - Hung Up on a Dream