We know what you're thinking, but no there doesn't seem to be a Pentium 4 666 as part of Intel's future numbering plans. Instead, it is releasing chips with 2MB of cache, numbered the 640, the 650, the 660 and the 670.Source: The Inquirer
These chips appear to have Intel's version of "cool and quiet" and no doubt will have the NX flag implemented too.
Intel to launch Pentium 4 6xxx series in early 2005

A French site saw some new roadmaps of Intels, and says that the company will launch a Pentium 4 6xx series in early 2005.