There is an alternative, more complex scoring method for Gin Rummy. It is said to have been devised by Hollywood celebrities back in the day (~1950?), so it's known as the "Hollywood Scoring" system. For those who just can't get enough of Gin Rummy, Hollywood scoring essentially allows you to play three games at once.

The score sheet is divided into three sets of double columns. The columns are headed up with the initials of the players. When a player wins hand #1, the score is recorded in the first columns. When s/he wins hand #2, the score is recorded in the first and second columns, and the score for hand #3 is recorded in all three columns. Whenever the scores in a column add to the agreed amount (usually 125, as noded above), that column is crossed off, the final score noted, and no more scores are added to that column.

The games could be played simultaneously (with several decks of cards), or could be played in rotation (game 1, game 2, game 3, then back to game 1). More games than a mere three could be played, following the same principle. If you have a lot of time on your hands, this method of scoring is adaptable to Spite and Malice.