CMB spectra and the SNIa luminosity-redshift curves point to the existence of Dark Energy (DE). However, these particular observables have difficulty distinguishing between models with the same average value of the DE equation of state. The Integrated Sachs-Wolfe (ISW) effect is a qualitatively different and, in some respects, a more sensitive probe of DE properties. I will discuss how the cross-correlation of the CMB temperature anisotropy with large scale structure, which is a measure of the ISW effect, can be used to break degeneracies between DE models.