Q Magazine, a rock oriented British music magazine, in their most recent issue (at least the one now on the stands in Canada), has a list of the 100 most powerful people in music. Their website does not have articles online but this is want I remember from checking it out at the bookstore.
Britney Spears is the highest ranked woman on their list at #17. Most of those ahead of her are industry types like Clive Davis (chief music man at BMG), Edgar Bronfman (head of Warner Music), Lowry Mays (head of Clear Channel), and the like. There are only a handful of male artists ahead of her like Fitty, Chris Martin, Andre 3000 and Eminem (#1).
Not bad for someone whose career is supposedly over and this is from a Britsh rock magazine, not Tiger Beat.
Britney gets repeated as a factor in the placement of several others such as Justin (in the 30's), Christina (in the 40's), Cathy Dennis ("Toxic" writer) and Joseph Kahn ("Toxic" director).