As Swagger Paris suggests, Summer's favorite cover-up is the denim vest! Varying washes, studded embellishments, or cool graphics update this old classic.
image source: http://blogs.glam.com/glamchic/2009/07/13/the-denim-vest/
image source: http://www.swaggerparis.com/2010/06/04/summer-must-have-denim-jacketvest/