However, DLP has its own problems (the rainbow effect is awesome!). LCoS is just another LCD-based technology (assuming I understood the wiki page on LCoS correctly), just with the LCD directly mounted on a mirror instead of projecting through it (and therefore I assume it has the same problem with light getting through "black" as a through-projection LCD). The Wikipedia article on LCoS has an uncited statement that LCoS is better contrast than projecting through an LCD, but doesn't mention black level at all.
LED backlights are no good on very large panels, because they use LED strips around the edge or on one side and a large light diffuser, which still produces an uneven result at large panel sizes. ELP is far better (it's a full panel sized light over the whole display), but far more expensive, and can still have trouble getting even illumination.