The (a) is because I am an idiot and forgot someone else (though it's more of a waiting for the proper spot to have him and then forgetting about it than just glossing over his name like I did with Withey. Anyways), but Sherron Collins is certainly deserving of the 13 spot by himself.
Let's start with the bad: he ended his career on an extremely sour note, going 4-15 with 5 turnovers in KU's 2nd round loss to Northern Iowa in 2010. It's probably fair to say if he got Cole Aldrich, the Morris twins, or Xavier Henry more involved, Kansas probably wins that game and potentially has another Final Four or national title run.