I can sing along with some, and just enjoy listening to others. They are all absolutely amazing.

• Dr. Horrible's Sing-along-blog
• Harry Potter and the Philosopher's Stone (although I love them all)
• Sweeney Todd
• Across the Universe (what got me into The Beatles)
• Les Choristes
• Juno
• Disney Movies
  • Beauty and the Beast
  • Hercules
  • Tarzan
  • Mulan
  • Hunchback of Notre-Dame
  • Princess and the Frog (particularly "Friends on the Other Side")
  • Tangled ("I see the light" is sew kewt! :3 )
• Sound of music
• Grease
• Hairspray (I prefer the original)
• Slumdog Millionaire
• Les Triplettes de Belleville
• Singin' in the Rain

Theatre

• Une Comédie Musicale
• Notre-Dâme de Paris
• Phantom of the Opera
• A Very Potter Musical (and sequel)
• Les Misérables