you're asking for someone who will win 20 games, have a WHIP around 1.00 and a sub-3.00 ERA and can be had after the 10th round in most 12-team drafts?
that's a tough one.... A couple of the guys already mentioned have that much potential, like King Felix, Beckett, and MAYBE Patterson, but do people honestly think Kevin Millwood will suddenly turn in to a dominating pitcher? Common, the guy's a location dude, and he's no Greg Maddux or even Tom Glavine for that matter. Same thing goes for most of the other people listed on this thread. I mean, I guess I could see Contreras doing something if he can pitch like he has in the second half over the course of a full sesaon, but even then he'd have to IMPROVE over his best numbers to date and maintain it for twice as long to get to the place Willis and Carpenter have this year.
Outside of the four mentioned above, the only other player I could see doing it is that young pitcher from SF. No, not Noah Lowry, sillies! I'm talking about Matt Cain. He's been a highly-touted prospect for a while now, he's got NASTY stuff, and in 6 starts this year, he's 2-1 with a 2.01 ERA and a 0.88 WHIP. His BAA is .133.
Do I expect Cain to win 20 next year? Hells na. He's still walking WAY too many people, and until he gets that under control, he'll have issues. But I think he's one of the few guys you'll be able to get later in your drafts who has the kind of potential needed to keep an ERA under 3.00 for a full season.