Two systems that use height channels, Dolby Pro Logic IIz and DTS Neo:X, which matrixes a front left and front right height out of the front left and front right channels. According to Dolby, non-directional ambient effects such as rain and wind are mapped to the height channels. This is similar to what is mapped to rear surround channels.
DTS-HD is a format which supports virtually any amount (over 2000) discrete channels for which a demonstration of an 11.2 system using four height channels was given at a Consumer Electronics Show.
Tomlinson Holman's 10.2 surround sound, a format currently under development, uses 12 or 14 fully discrete channels, both including two height channels; front left and front right.
The Dolby Atmos surround system, which allows for unlimited number of tracks, uses height channels too.