It sounds like
The Shins. The way the song changes like you said make me think that. Here's a few it could be...
This is one of my favorite songs. It has a tad bit of drums but sort of fits the profile
New Slang
http://www.youtube.com/watch?v=QD7qIthSdkA
Turn on Me
http://www.youtube.com/watch?v=bIRmyfKOAfM
Simple Song - this one's the most recent
http://www.youtube.com/watch?v=RoLTPcD1S4Q