  We employ Coleman-Weinberg and Higgs potentials to implement inflation in
non-supersymmetric grand unified theories (GUTs) such as SU(5) and SO(10). To
realize a scalar spectral index close to 0.96, as indicated by the most recent
WMAP 5-year anlaysis, the energy scale of observable inflation turns out to be
of order $10^{16}$ GeV. This implies a GUT symmetry breaking scale of similar
magnitude, and proton lifetime of order $10^{34}$-$10^{38}$ years. In some
SO(10) models with axion dark matter, the scalar leptoquark boson exchange
leads to proton decay with a lifetime of order $10^{34}$-$10^{35}$ years.
