My choice is Kristen Bell.. she might be 26 but she looks like shes 20
so shes perfect for a Post-crises Kara.
she can do the bored little girl this aswell ..
the only problem is that she is a tad bit short.. 5'1.... Routh is 6'2 :P
(and as you saw in the picture on page 2 or 3 .. Tom Welling is alot taler.. at 6'3 (same as me))
the funny thing is that she auditioned for the role of Chloe Sullivan on smallville :P