All of these players will undoubtedly be drafted, most of them highly and possibly as first rounders. I'll give most guys an NFL comparison, some I've dreamed up, others I've read (maybe on TheBigLead) or heard elsewhere. Here's my thoughts on the more notable guys that I'm focused on (I don't know a ton about some of the guys near the bottom of the list):
Michael Crabtree is the star of this show and in my mind, will be an outstanding pro right out of the gate. He's smooth in his routes and has tremendous game instincts. Couple that with great size, strength, and speed and he should fit well into the NFL. Possible NFL comparison: Andre Johnson. He is just as physically imposing and should be able to take over games at the next level just as Andre does now.
Julio Jones is a big part of Alabama's dominance this season because he does it all for QB John Parker Wilson. Jones is a physical monster who reminds many of Terrell Owens but I don't think he is as naturally powerful. However, he has great hands, which is something T.O. rarely hears praise about. NFL comparison: Brandon Marshall. He's not the route runner that Marshall is, but he's got all the physical tools.
Jeremy Maclin just looks like a star college receiver. He's tall, lean, and a bolt of lightning in the open field. He just embarrases opposing defenders in space and gets to a second gear that most players just don't have. NFL comparison: DeSean Jackson. Maclin's got much better size, but he flashes that same game-breaking speed and quickness. He's dangerous coming off screen and reverses, also much like DeSean.
AJ Green is a dynamite freshman who manages to shine despite playing alongside Matthew Stafford and Knowshon Moreno. He's got a great size/speed combo that is simply too much for most college CBs to handle. His route-running needs work, but that will come with time. NFL comparison: Larry Fitzgerald. Green's hands and body control are exceptional which should make him very successful, like Fitzgerald.
Percy Harvin is lighting fast and explodes in and out of cuts up and down the field. He is extremely versatile with tremendous agility and quickness. NFL comparison: Santan Moss (props to TheBigLead for a good spot). Harvin will get more looks out of the backfield than Moss does but he is equally as explosive and short in stature as Moss.
Derrick Williams does it all for Penn State and has all of the necessary tools to be a good pro. He receives it, rushes it, and returns it, all extremely well. But what sets him apart is the mental aspect of his game. Williams is an extremely hard worker on and off the field. He does all the little things right: route-running, blocking, reading defenses, etc. Also, he possesses 4.3 speed and decent size at 6' 200 lbs. NFL comparison: Reggie Wayne. He has all of Wayne's best attritubes in his smarts, body control, and adept ability for getting open. I think Williams will be better utilized in the NFL than he currently is at Penn State and his stock will rise greatly at the combine later this year.