What flower is this blue flower?
Without more detail about the whole plant (including leaves), where it came from, and about whether or not it was spray-painted, watered with dyed water, etc. it would be difficult to ID. 

It seems to be in the Asteraceae family, and in the pompon class, as seen in these vender's pictures. (Disclosure: I have no affiliation with the company.)

http://www.fiftyflowers.com/product/Blue-Cushion-Bulk-Flower_10.htm
http://www.fiftyflowers.com/product/Blue-Cremon-Bulk-Flowers_24307.htm
http://www.fiftyflowers.com/product/Electric-Blue-Flowers_10.htm

It is most similar to a blue chrysanthemum.


http://john-hallett.co.uk/2013/04/04/blue-crysanthemum/



Sources:


as listed above for images
http://en.wikipedia.org/wiki/Chrysanthemum (pink image)
http://www.mums.org/chrysanthemum-classes/