The generally very useful and interesting book Bologan's Black Weapons suggests the following line as a practical way to meet the Evans Gambit.
[FEN ""]
[Title "Evans Gambit"]
[Startply "12"]
1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. b4 Bxb4 5. c3 Ba5 6. d4 b5!? 7. Bxb5 Nxd4
The line continues 7. Bxb5 Nxd4 8. Nxd4 (8. Nxe5 is less good, see analysis in the book) exd4 9. Qxd4 Qf6 with reasonable play for black.
However, the book doesn't mention the move 9. O-O !?.
[FEN ""]
[Title "Evans Gambit"]
[Startply "17"]
1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. b4 Bxb4 5. c3 Ba5 6. d4 b5!? 7. Bxb5 Nxd4 8. Nxd4 exd4 9. O-O!? (9. Qxd4 Qf6) dxc3 10. Bc4!
In a blitz game I played as black, I thought I should prevent white from building a big center with cxd4, so I played 9... dxc3. But then after 10. Bc4! I had a very bad position.
So my question is, what should black play after 9. O-O !??