The second half comeback in that 2007 OSU-Tennessee NCAA tourney game was unbelievable. That's gotta be on the list. I've also got a couple more that haven't been mentioned that I think are worthy for consideration.
1999 Ohio State-Auburn (NCAA regional semifinal): Some might argue that the game against St. John's (and Ron Artest) in the regional final was better, considering what was at stake, but the mountain OSU had to climb in the previous game will go down as one of the best wins in Ohio State basketball history.
Few expected Ohio State to beat Auburn. Ohio State was very talented, but that Auburn team was something special. Without question, that was the best season in the history of Auburn basketball, and many thought they would clinch their first-ever final four appearance. Of Auburn's 29 wins that season, all but two were by double-digits. They earned a #1 seed, suffered just 3 losses (2 against SEC tourney champ Kentucky), and Chris Porter was an absolute monster. The game was played in Knoxville in front of 24,000 fans, and the overwhelming majority (~20,000) were in Auburn's corner. The Tigers had a distinct size advantage, and the Buckeyes were in foul trouble the entire game. The Buckeyes led for most of the first half, but mounting foul trouble swung momentum in favor of the Tigers midway through the second half. In the end, it was the Buckeyes stellar defense in the final three minutes that was the difference - with 3 minutes left and the score tied at 61, Auburn wouldn't score again until a garbage 3 by Doc Robinson with a few seconds left. Scoonie Penn and Michael Redd took control of the game in the final minutes, finishing with nearly 50 points combined.
The Auburn faithful was visibly angry and dejected. Fans were tearing up their regional final tickets as they were leaving Thompson-Boling Arena. My dad and I scalped seats for cheap behind the basket for the game against St. John's. The tone of the regional final ended up being a lot different than what was originally seen as a Maryland-Auburn matchup. Buckeye fans flooded the arena for the following game, although it was a few thousand short of a full house. Happy to say that I got to see both of those great games up close.
1985 Ohio State-Iowa: I was only 3 years old at the time, but my dad loves talking about this one. Chris Spielman was a man among boys that night.