Len Bias is the first guy I really remember, but I was young, and access wasn't nearly like it is now.
I have very vivid memories of Derrick Coleman. And more still of Chris Webber, Shaq, and all three Duke guys from that era, Hurley/Hill/Laettner, all of whom I hated, and Jamal Mashburn.
Given the choice of all the guys I remember watching in college as pro prospects, not knowing how their careers would wind up, I'd go Shaq, Bias, Webber ahead of anyone else I can think of. Coleman would be up there too, but probably behind Duncan and maybe a few others.