Talkin' Balls is a magazine featured in Grand Theft Auto IV.
It is a magazine about football, baseball, hockey, basketball and other sports. Their headquarters are based in the Liberty Sports Network building in Star Junction, Liberty City. The name is another example of Rockstar's crude humor, because "balls" refers to testicles.
It is likely a parody of Sports Illustrated, or more accurately ESPN Magazine, which is owned by the sports network ESPN, similar to the way Talkin' Balls is owned by the Liberty Sports Network. It can easily be found in Newspaper Stands. In the prologue of Grand Theft Auto V, there is a copy on a bench in the building that Trevor, Michael and Brad rob.