I wanted to make this a separate category because projecting players this young usually requires a crystal ball and unfortunately, I don't have one. However, the following players clearly have a headstart in making it to Cooperstown.
Miguel Cabrera Cabrera will follow in Vlad and Manny's footsteps. He's a monster already and will only get better. Barring injury, there's about a 95% chance Cabrera will make the HOF.
David Wright Wright is 22. He has 29 career home runs. He's hitting close to .300 as a third basemen. I don't think he could ask for a better start to a career. Based on his age and how good he is right now, I can't say with confidence that he won't make the HOF.
Jake Peavy Peavy will probably win more than his fair share of ERA titles. He's an awesome pitcher. It might help if he got out of San Diego but I actually think he'll make it.
Dontrelle Willis Willis is only 23 and he already has 38 career wins. He has struggled mightily in the second half in every season he's been in the majors. If he gets that worked out, he has a great start to a possible HOF career.
Hank Blalock Blalock has produced ever since the Rangers put him in the lineup. He's only 24 but he already has 83 career home runs. He could make a run at 500 which would be a lock for a third basemen.
Huston Street Street is phenomenal. In his first season, he has a 1.41 ERA and a .98 Whip. He's only 21 years old.
Francisco Rodriquez Frod is the heir apparent to Mariano Rivera. At 23, he's already one of the dominant closers in baseball.
Jeremy Bonderman Obviously, Bonderman is the hometown favorite. He's started off young enough. One minor setback is that he's 9 games under .500 for his career. His ERA took a tremendous hit in his first two seasons. In any other organization, "Bondo" would be make his debut this season. The 2003 Tigers were so bad that a 20 year old rooke fit right in.
Mark Prior Prior is the injury machine. I honestly don't remember Prior when he was his dominant self. It seemed so long ago. I think Kerry Wook has rubbed off a little on Prior. If he can ever stay healthy, Prior is as good as any pitcher in the league.
Joe Mauer Mauer is the best young catching prospect in baseball. He's been decent in parts of two seasons with the Twins. I think he'll be one of the best catchers over the next 15 years but I don't think he'll make the HOF.
Justin Morneau Morneau is good but Mark Grace was good too. John Olerud was also good. I think Morneau has a lot of Grace and Olerud in him.
Rich Harden Harden is as good as any young pitcher in the game. His numbers this season have been phenomenal. He's 9-4 with a 2.54 ERA and a 1.08 Whip. The most impressive number is his .206 batting average against. He's only 24. Harden has a very good shot if he can stay healthy.
Zach Duke Duke has only had seven starts. He's 5-0 with ridiculous numbers. Everyone else on this list has done more than Duke but I don't want to look foolish in 20 years by not having him on the under 25 list.