Let's stop saying "third party"...
... and start saying "emerging parties" (hat tip, DCBlogger, in conversation).
Well, for one, thing, "third party" assumes that there are two other parties when, in fact, the two legacy parties are better thought of as a single, self-reinforcing system -- composed, granted, of two teams or tribes that hate each other (and us) -- rather than as separate entities that oppose each other on policies that would make our lives better.
For another, "emerging" has a very, very nice ring to it. And "emerging" implicitly distinguishes green and/or independent activity from Astroturf organizations like the Koch-funded faction of the tea parties, or OFA.
So, not D, R, and "third parties," but "legacy parties" and "emerging parties."