• Chris Polk - Lead Guitar, Van Dorn Street (Vol. 1)
  • Robinson Lee Earle & Sara Mosher - Acoustic Guitar & Vocals, East Falls Church (Vol. 1)
  • Seth Kibel - Flute, Ice Skating at the Archives (Vol. 2)
  • Matt Slaughter - Chorus Voice, Clarendon (Vol. 2), Drum Machine, Deanwood (Vol. 4)
  • David McLaughlin - Banjo & Mandolin, Tenleytown (Vol. 3)
  • John Simmons - Rickenbacker 12-string, Tenleytown (Vol. 3)
  • The Six Degree Singers, dir. by Rachel Carson - How an Afternoon Dream Caused Her to Miss Her Stop at Silver Spring (Vol. 3)
  • The Williams PipeTone Organ at Congressional Cemetery - Potomac Ave. (Vol. 3)
  • Louis Loman (percussion), Ken Francis Wenzel (sax), Molly Hagen (voice), Rachel Levitin (voice) - Deanwood (Vol. 4)
  • Maureen Andary, Sara Curtin (The Sweater Set) - Lyrics, Vocals, Flute, Ukulele, Bells - Strathmore (Vol. 4)
  • Jonny Grave (slide guitar), Terry Boes (harmonica) - Union Station (Vol. 4)
  • The Blue Angelinas - Blue Angelina I - IV & Twinbrook (Vol. 5)
  • Alissa Moore (violin), Bill Martien (guitar), of Star FK Radium - Stadium/Armory (Vol. 5)
  • Alexander Grushin (poetry) - Twinbrook (Vol. 5)
  • Cathy DiToro (voice) - Prince George's Plaza (Vol. 6)
  • Ken Francis Wenzel (sax) - Prince George's Plaza (Vol. 6)
  • Anders Fahey (banjo) - Spring Hill (Vol. 6)
  • Sam Snow (beats) - Court House (Vol. 6)
  • Ardamus (lyrics & voice) - Shaw (Vol. 6)