Generations Dirge, and to a lesser extent Blurr and Red Alert.
After the BotCon 2007 fiasco, Hasbro didn't have to make a Dirge, but they did. They also gave him the best (IMHO) deco out of all the coneheads. With the $10 sale on now, anyone who likes Classic Decepticons should have one; he's easily worth $10.
I don't know why Blurr is also pegwarming. He's a cool blue car with guns; what's not to like? And with Henkei Red Alert going for $50+ why aren't collectors snapping up the much cheaper and just-as-good Hasbro version? Is the red head that important? (The Henkei version's head is molded in black plastic too; it's just painted red.)
And RTS Lugnut shelfwarms too despite being all kinds of awesome. Granted his colors are off, but there's no guarantee there will ever be a purple one. The recent $15 sales should have had him flying off shelves.