Sunyaev-Zeldovich effect has major effect on the CMB spectrum at large angular scales, but is easy to correct for. The kinetic Sunyaev-Zeldovich effect is much
harder to correct for, but is very small. ¥Extragalactic radio
sources make small but ultimately unimportant
contributions to CMB up through large angular scales
(but are interesting in and of themselves). ¥Far-infrared sources
deserve more study, but will also probably
require only minor corrections to newer measurements
of the CMB. ¥Planck and MAP will answer many of our questions about the CMB, and should be able to bypass most foreground sources.