GDot.com is a good quality 4-character name, even has some Overture for "g dot" (or "dot g", Overture doesn't specify). I think you may be able to find a buyer willing to pay low to lower-mid $xxx on this one. Any more than that would have to be an end user that REALLY likes it, and you'd either be lucky or waiting a few years for that bid.
AdSponsor.com is a decent name too, though would need to be developed IMO to really see more than mid to high $xx (possibility of more to an end user of course). Good luck with the names.