15 Central Park West
How can a list like this not include this megaflip haven (pictured above)? To wit: This spring, a venture capitalist paid $13.8 million for a unit the seller bought just two months previous for $6.9 million, according to trade publication the Real Deal; a 29th-floor apartment — picked up for $7.3 million — went for nearly $14 million; and a cable mogul who bought his 36th-floor spread for $7.34 million is now on contract for somewhere near its $12.5 million price tag.

134 Charles Street
The house just fetched $17 million for its former owner, who bought it in 1989. City records don't reveal what she paid in total, but the $100,000 mortgage filed with the city eight days after signing the deed gives an idea of just how much this deal paid off.

Photo: Newscom

777 Washington Street
Photographer Albert Watson needed a live-work space in 1985, so he purchased this refrigeration plant for $850,000 and transformed it into a showplace. It proved a good investment; he sold it this spring for $34 million.

19 Gramercy Park
Designer Richard Tyler and his wife, Lisa Trafficante, scored this mansion (equipped with its own key to the park) in 1985 for $3.5 million. Fifteen years later, they parlayed the fascinating property into a then- and still-impressive $16.5 million. Amazingly, they repeated the feat once more with the Washington Street townhouse they bought post–Gramercy Park for $6.1 million, which they recently sold for $14.4 million.

Photo Courtesy Brown Harris Stevens