One of my favorite songs is Stairway to Heaven. 
I came close to playing it last Spring but the original version is pretty long and gets fairly loud near the end.  I was concerned that might be a bit too much considering the mental state that many people find themselves in at the end of the spring semester.  It might be the perfect choice for the first day of classes next Fall in the 8 am section - mainly because the song is pretty long and gets kind of loud near the end.
Here's a nice version of Stairway to Heaven by two Mexican guitarists: Rodrigo y Gabriela.  If you like that then check out Diablo Rojo by the same group (another good choice for the 8am class - it'll get their blood circulating)

Une Americaine a Paris by a group named Rupa and the April Fishes is one of the most unusual songs I've found so far.  It's also sung in French, what more could you ask for?  While learning a little bit about Rupa and the April Fishes I found mention of a group called Pink Martini.  They've done a lot of pretty sultry stuff.  Listen to Una Notte a Napoli and Hey Eugene.

xxx Along Again Or  xxxx Si Tu Disais xxx  by a local Tucson group named Calexico. 
Another local group is Tesoro xxx