Another Week

It's time for our second Week within the Month of Musicals! It's called: The Series Week. Yes, each song this week (Monday to Friday) is from a series. Or show, but the term "show" could also encompass everything this month.
Anyway, we're starting with Glee and getting it out of the way.
One of my favourite songs from it is the mash-up of "Halo/Walking on Sunshine." I don't know why the mash-ups aren't on any of the CDs that have been released, but they're not, and that's just too bad.