The Hubble expansion, the Cosmic Microwave Background Radiation(CMBR) and the primordial Big Bang Nucleosynthesis(BBN) are three cornerstones of the standard hot Big Bang cosmological model. Recently these three kinds of observations have been making a strong case for the existence of a nearly uniform component of dark energy with negative pressure: More than twenty experiments of CMBR measurements have now covered three orders of magnitude in multipole number, and are beginning to define the position of the first acoustic peak at a value that is consistent with a flat universe [1]; However, the deuterium abundance measured in four high redshift hydrogen clouds seen in absorption against distant quasars [2] combined with baryon fraction in galaxy clusters from X-ray **data** [3] give a low matter density universe, Ω m ∼ 0. 3-0.4; The discrepancy between the low matter density and a flat universe is observationally resolved by high redshift Ia type supernovae (SNeIa) observations [4], which implies an accelerating universe driven by a dark, exotic form of energy component. For a recent review of observational evidence for the dark energy component, reader is referred to Ref. [5]. It seems that determining the amount and nature of the dark energy is emerging as one of the most important challenges in cosmology.