The Max Lange Attack
1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. 0-0 Nf6 5. d4!?
exd4 6. e5
Here are some theoretical games. Max Lange successfully played this in the mid-1800s, and it has been popular ever since. You also need to know the Max Lange Gambit, in case they play 5. Bxd4.