  Much recent work on the cosmic microwave background (CMB) has focussed on the
angular power spectrum of temperature anisotropies and particularly on the
recovery of cosmological parameters from acoustic peaks in the power spectrum.
However, there is more that can conceivably be done with CMB measurements. Here
I briefly survey a few such ideas: cross-correlation with other cosmic
backgrounds as a probe of the density of the Universe; CMB polarization as a
gravitational-wave detector; secondary anisotropies and the ionization history
of the Universe; tests of alternative-gravity theories; polarization, the
Sunyaev-Zeldovich effect, and cosmic variance; and tests for a neutrino mass.
