¥The thermal 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.