Since adding my 2 cents will take us to $653080.34.
What my ad would look like:
A montage of 3 short vignettes with three women who supported Hillary Clinton, each representing a different Hillary demographic, e.g. One older woman, one latino/latina etc.
The first says: I voted for Hillary Clinton in the primary, but I'm now proud to support Barack Obama. He can deliver on the issues that are important to Democrats like Hillary and me.
The second makes clear that McCain opposes Hillary's agenda. You get the picture, you could basically cut and paste bits out of Hillary's convention speech.
Then the kicker: end with a picture of Obama, "I'm Barack Obama, and I approve this message." Then a picture of Obama and Hillary together, "And I'm Hillary Clinton, and so do I.
I'm no professional, but the end to me is unusual enough that it sticks in your memory and gets media bobbleheads talking.