  In this paper we determine the constraints on cosmological parameters using
the CMB data from the WMAP experiment together with the recent power spectrum
measurement of the SDSS Luminous Red Galaxies (LRGs). Specifically, we focus on
spatially flat, low matter density models with adiabatic Gaussian initial
conditions. The spatial flatness is achieved with an additional quintessence
component whose equation of state parameter w_eff is taken to be independent of
redshift. Throughout most of the paper we do not allow any massive neutrino
contribution and also the influence of the gravitational waves on the CMB is
taken to be negligible. The analysis is carried out separately for two cases:
(i) using the acoustic scale measurements as presented in H\"utsi (2006), (ii)
using the full SDSS LRG power spectrum and its covariance matrix. We are able
to obtain a very tight constraint on the Hubble constant: H_0 = 70.8
^{+2.1}_{-2.0} km/s/Mpc, which helps in breaking several degeneracies between
the parameters and allows us to determine the low redshift expansion law with
much higher accuracy than available from the WMAP + HST data alone. The
positive deceleration parameter q_0 is found to be ruled out at 5.5 \sigma
confidence level. Finally, we extend our analysis by investigating the effects
of relaxing the assumption of spatial flatness and also allow for a
contribution from massive neutrinos.
