The Tampa Bay Lightning introduced a massive 28'x50' centrehung video scoreboard this season. (Not that their old one was small -- it was already one of the biggest in the league at 16'x28'.) The sides facing the end zones are a narrow 28'x20'. It's a Daktronics board. The shot above is a mock-up. Here's a video showing the scoreboard in action.
Quite a similar design in Houston at the Toyota Center where the Rockets play. This one is 25'x58' feet, so just a bit bigger than the one in Tampa Bay. It's a Panasonic board and they claim it's the "largest combined viewing area of any indoor center-hung scoreboard currently used in the U.S." Here's more about the installation. And here's a video. (Look at all those stats!)
Meanwhile in the MLB, the Seattle Mariners claim that they will have the biggest scoreboard in baseball this year. 56.7' x 201.5 feet wide. That's as wide as an NHL rink. "The viewing area will be equal to about 2,182 42-inch flat screen TVs." It's being made by Panasonic.
An article on the Mariners web site also offers these stats on other large video displays in MLB:
Comparison to MLB Video Screens
Safeco Field, Seattle Mariners: 56.7' x 201.5' - 11,425 sq. ft.
Kauffman Stadium, Kansas City Royals: 105 x 84' - 8,820 sq. ft.
Citizens Bank Park, Philadelphia Phillies: 76' x 97' - 7,372 sq. ft.
Minute Maid Park, Houston Astros: 124' x 54' - 6,696 sq. ft.
Comerica Park, Detroit Tigers: 94' x 65' - 6,110 sq. ft.
Bonus stat (Cowboys Stadium, Ft. Worth, Texas: 160' x 72' - 11,520 sq. ft.)
Reliant Stadium (home of the Houston Texans) will lay claim to the widest scoreboard in pro sports, when they unveil a board measuring 52.49'x277.17'. They're hoping it will help them win a bid to host the Super Bowl. Manufactured by Mitsubishi.
I don't know the source of this infographic or how accurate it is but it's a decent visual to compare the different stadiums.
What other big scoreboards are being installed this year?
