Scott. There definitely has to be a distinction powered and unpowered and then needing a sub or not. And then there is the question of sound quality which the Sonos Playbar is just average at best. The problem is people like it but just don't realize how much better sounding stuff is out there. I too am looking for one.
To keep things manageable, I've decided to limit this guide to powered soundbars, because they serve best as a replacement for the TV's onboard audio. As for subwoofers, the vast majority of soundbars need one to sound their best—the only ones I'm considering for the guide that probably don't are the Atlantic Technology 235 with H-PAS technology and the Zvox 580, and maybe the SpeakerCraft CS3. From what I've read (including a review just posted by imagic on AVS), the Sonos Playbar actually sounds very good as long as you include the Sonos Sub. Many AVSers have recommended including the PlayBar in the guide, and many pro reviewers also include it in their top soundbar lists, so I think I'm going to include it (along with the sub) as well.