The greatest comeback I ever saw was Alex's against Shane a few years ago. It was a Race to 100 and Alex trailed 67-45. I think the final score was 100-92 Alex. Alex played perfect pool for 5-6 hours; run-out, run-out, run-out; from everywhere and anywhere!
One of the best played matches I ever saw was when Shane played Alcano for the hot seat at the U.S. Open back in 2007. Shane played some super pool on a very tough Diamond table. Ronnie was playing good but Shane just shut him down. Another remarkable match that I witnessed was at the World Ten Ball a couple of years ago. It was between Lee Vann and an Asian player named Lung (Taiwan?). Lung was well ahead, something like 9-3 going to eleven. It looked like it was all over. Lee Vann proceeded to put on an uncanny shooting display to come back and win the match. Lung didn't make any mistakes. It was just a case of Lee Vann shooting the lights out.
One more that sticks in my mind is the semifinal of last year's World Cup between Team Philippines (Orcullo and Gomez) and Team Taiwan. What an exciting and well played match by both teams. I was jumping out of my seat doing commentary. I've tried and tried to get a copy of that match to no avail. Both teams kept coming up with shot after shot and it went down to the wire naturally. The Finals was anti-climatic after that match.
Almost every year at the Mosconi Cup there is some amazing play by both teams, now that the teams are so evenly matched. The last two years (post Earl era) have been the best played Mosconi Cups of all time, and the most exciting. If you want to see some of the best pool played all year, come to the MGM in December. All I can say is see the Mosconi Cup once before you die. It is the best event in Pool!