I started using Curves (Photoshop CC) to adjust the Blue Chanel and then the same curve to adjust RGB values to obtain a bluer sky.
http://i64.tinypic.com/2ziymax.jpg
Result:
http://i65.tinypic.com/ic0g9j.jpg
I also add blue Chanel saturation.
There must be a better way to get a blue sky without over-saturating all colors and/or causing color shifting. But I don't know what that may be...?