patzer2: <Shadout Mapes> Good catch on 21. Nxf6+? losing. Appreciate the catch. You can tell no thought or analysis went into those off hand recommendations.
21 Nc5? is also a lulu as it gets clobbered by 21...Qd5!
Honza Cervenka's 21. Qc7! is definitely the best move according to computer analysis. It allows white to hold the extra pawn after all black tries, as the white queen can interpose with advantage to stop the black queen's double attacks and mating threats. For example:
21 Qc7 Qd5 22. Qc4 Be6 23. Qxd5 Bxd5 (1.16 plus score)
21 Qc7 Qa6+ 2. Qc4+ Qxc4+ 23. Rxc4 Kf8 (if 23...Bf5, then 24. Rc5) 24. Ra4 a6 25. Nc5 Rb8
(1.18 plus score)
21. Qc7 Qd7 22. Qxd7 Rxd7 23. Rc3 Kf7 24. Nc5 Re7 25. Kd3 Bg2 26. f4 (1.04 plus score)
(computer analysis from chesslab.com)