Recent detection of the Integrated Sachs-Wolfe effect via cross-correlation of the CMB with large scale structure provided another piece of evidence for the existence of Dark Energy. Although cross-correlation measurements are limited by large statistical uncertainties, they probe physical processes that are only weakly constrained by the CMB spectra and the SNIa luminosity curves. I will show that the cross-correlation data, combined with the CMB power spectra, can provide competitive constraints on certain properties of dark energy.