The 1975/Japanese House/Wolf Alice - 5/17 Governors Ball - 6/3 - 6/5 Wolf Parade - 6/9 Taste of Chaos Festival - 6/18 The Stone Roses - 6/30 Noel Gallagher - 7/5 Coldplay - 7/16 Flight of the Conchords - 7/24 Paul McCartney - 8/7 Blink 182 - 8/13 FYF Festival - 8/27-8/28
I know Baroness has gotten away from the very heavy side of their music, but I still would call it neither "chill" nor "relaxing." I'll give what seems to be the 8th suggestion for Beach House. In addition I think Father John Misty, Cat Power, The xx, and Wild Nothing all come to mind as either chill and relaxing.
If you want chill but 'heavy', check out Trixie Whitley. She played the sonic stage last year, I caught her in NY at a small show as well and got to talk with her. You would not believe the voice on this woman. She's been working with Daniel Lanois for his Black Dub project...http://www.youtube.com/watch?v=e255MtrXG7g
Her solo stuff is a little different. Still an unbelievable talent. If you get the time, check out her father, Chris Whitley. One of my all time favorites.