Here's a few suggestions I would find interesting, obviously all of them shouldn't be added but it's just what I am thinking.
Larger Avatars - 160x170 + 500kb
Contributor Award - Something like this
A little userbar under the persons name like Jay posted.
A selection of readable name colours to choose from - Dark Blue, Purple, Red, Green, Rainbow
Larger Inbox - Allows 50 extra incoming/outgoing private messages
Ability to see who viewed your profile