To expound on my answer (for the guy who is 5 years older than me acting like he's been around since the 50s) note the words "I think" before the post. Obviously my exposure and knowledge is limited.
Earl Campbell - Having grown up with a very good friend whose father was a good friend and business partner of The Tyler Rose I was fortunate enough to watch quite a bit of mid-1970s Texas Longhorns football on tape, some of it old-school reel film in Mr. Campbell's living room. Also being around the program to a small extent has given me a bit of (biased) insight. He always dominated, it wasn't even fair.
Bo Jackson - I don't think this one even needs justification. I was 1 when he was a freshman in college but I was quite into sports during his heyday in the professional leagues. And as one might guess, they occassionally referenced his NCAA days.
Herschel Walker - I grew up an avid Cowboys fan, see above.
Randy Moss - See the first sentence of the Bo Jackson explanation.
I remember thinking Ricky Ervins of USC would be a superstar. Silly. You might remember him, though, he kicked Michigan's ass in a Rose Bowl some years back.