+5  A: 

To your ComboBox add

SelectedValuePath="Key" DisplayMemberPath="Value"
Bryan Anderson
I think you mean SelectedValuePath and DisplayMemberPath, those worked for me at least, thanks.
Edward Tanguay
Oops, yes I did. I'll fix the answer.
Bryan Anderson
A: 

I can't find SelectedValuePath for my SilverLight ComboBox! Am I missing something?

Thanks.

K.Kong