  The recently discovered correlation between the rest frame GRB peak spectral
energy $E_{\rm peak}$ and the collimation corrected energy $E_\gamma$ in long
GRBs is potentially very important, yet awaits confirmation from an independent
sample. It may help to shed light on the radiation mechanism of the prompt GRB
phase and on the way -- and in which form -- the energy is released from the
central engine. We here present some additional evidence for the correlation
(two new bursts) and re-derive the best-fit parameters. The tightness of the
correlation is confirmed (sigma=0.1 dex). We show that this correlation allows
us, for the first time, to use GRBs as cosmological probes to constrain the
expansion history of the universe.
