  (Abridged) We carried out an extensive search to identify the counterparts of
all the sources listed in the WMAP 3-yr catalogue using literature and archival
data. Our work led to the identification of 309 WMAP sources, 98% of which are
blazars, radio quasars or radio galaxies. At present, 15 objects still remain
without identification due to the lack of optical spectroscopic data or a clear
radio counterpart. Our results allow us to define a flux limited sample of 203
high Galactic latitude microwave sources ($f_{41GHz} \ge 1$ Jy, $|b_{\rm II}| >
15^\circ$) which is virtually completely identified (99%). The microwave band
is ideally suited for blazar statistical studies since this is the part of the
em spectrum that is least affected by the superposition of spectral components
of different origin. Using this data-set we derived number counts, luminosity
functions and cosmological evolution of blazars and radio galaxies at microwave
frequencies. Our results are in good agreement with those found at radio
frequencies. The 5 GHz bivariate blazar luminosity functions are similar to
those derived from the DXRBS survey, which shows that this sample is
representative of the blazar population at 41 GHz. Microwave selected broad-
lined quasars are about 6 times more abundant than BL Lacs, a ratio that is
similar to, or larger than, that seen at radio and gamma-ray frequencies, once
spectral selection effects are taken into account. This strongly suggests that
the mechanism responsible for the generation of gamma-rays is, at first order,
the same in all blazar types. Our results confirm the findings of Giommi &
Colafrancesco (2004, 2006) that blazars and radio galaxies are the largest
contaminants of the CMB anisotropy maps. We predict that these sources are also
bright gamma-ray sources, most of which will be detected by AGILE and FERMI.
