Devil's Island PinballA sixth table, Devil's Island, was made but not included with Balls of Steel. It was finally released in early 2000 as a seperate product - not an add-on. Also, it was distributed by Expert Software, rather than Apogee or GT Interactive.
Pinball WizardsPinball Wizards is actually a project group of Apogee. In 1997, Apogee decided not to develop/release games under their own name, but rather specialized divisions of themselves. Most of their new releases have gone under the roof of 3D Realms, but Pinball Wizards was created for Balls of Steel (after all, it's not 3D). As of 2011, the Pinball Wizards name was never used again.
ReferencesThe table "Mutation!" features catchphrases of C. Montgomery Burns from the TV Show The Simpsons done by a very similar voice.
References: Duke NukemThe first appearance anywhere of a pinball machine named "Balls of Steel" is in level 1, "Hollywood Holocaust", of Duke Nukem 3D. Since 3D Realms and Pinball Wizards are both divisions of Apogee, either this early appearance inspired the actual Balls of Steel product or was a leak / early promotion of their pinball video game that would come out of the pipe nearly two years later.
In any case, the references went both ways, as Balls of Steel includes a Duke Nukem 3D-inspired table, with ramps and bonuses named after Duke enemies (octabrain, pig-cop) and power-ups (jetpack, HoloDuke). Icing the cake is the recording of original Duke-y quips by Jon St. John, the official voice actor for the Duke Nukem character.
Information also contributed by Dmichal and Pseudo_Intellectual