3. "Mad World" by Adam Lambert. (Also Wise Guys and original sad Gary Jules version.)
4. "Hallelujah" - any version, but I'll post the John Cale version here.
5. "A Wolf At the Door" by Radiohead. (I don't even know why this one breaks me. It just does. It's also the only Radiohead song I listen to on purpose. Also, strong language in this one.)
7. "I Crush Everything" by Jonathan Coulton. (Yes, it's about a giant squid. That somehow doesn't make it any less sad.)