@wandeljw,
Did you consider 15 ... Nxg4 16. fxg4 Qh4+?
I kept looking at that move to get two pawns for the knight plus a great center attack on the e pawn, but I couldn't decide if having the bishops and rooks open on the king side was too much of a risk.
1. Nf3 Nc6 2. e4 e5 3. c4 Nf6 4. Nc3 Bb4 5. Nd5 d6 6. Nxb4 Nxb4 7. Qa4+ Nc6 8. d4 Bd7 9. Qc2 0-0 10. Bg5 Nxd4 11. Nxd4 exd4 12. Rd1 c5 13. f3 h6 14. Bf4 Bc6 15.g4 Ng4 16. fxg4 Qh4