THE OH HELLO'S: are a brother sister duo from Texas. They have a very acoustic, mumford & sons sound, creating a folk rock type sound. Their self-titled EP was released in 2011, and has a slightly Irish folk sound to it, if perhaps a little less upbeat jig like. (Please go and listen to all 4 of their songs if you click on their name, I honestly love them all... so addictive)
If I had to pick one (which is impossible) I will go with the more upbeat one called 'Trees':


O is also for OF MONSTERS AND MEN: They are slightly more well known band from Iceland. Their first EP album called 'Into the Woods' that came out in 2011, and then released their first full album called 'My Head is an Animal' early this year I think. They released a single called 'Little Talks' that went to number one in Iceland.
If you this song go and have a look at the album on the US itunes, I also really like the songs 'Dirty Paws' and 'King and Lionheart'

Love and Peace.