Answer by taking a quote from the following article:

Mental As Anything are an Australian new wave/pop rock band that formed in Sydney in 1976. Its most popular line-up (which lasted from 1977-1999) was Martin Plaza (birth name Martin Murphy) on vocals and guitar; Reg Mombassa (birth name Chris O'Doherty) on lead guitar and vocals; his brother Peter "Yoga Dog" O'Doherty on bass guitar and vocals; Wayne de Lisle (birth name David Twohill) on drums; and Andrew "Greedy" Smith on vocals, keyboards and harmonica.

Mombassa and O'Doherty formed the duo Reg & Peter/Peter & Reg (they alternated names whenever interviewed) and released a single, "Jean" in March 1991, before adopting the band name Dog Trumpet and releasing the album Two Heads One Brain. Studio musicians were Mike Gubb on keyboards (ex-Dynamic Hepnotics, Mental as Anything), John Bliss on drums (ex-The Reels) and Mark Honeybrook on bass guitar. Further releases followed with the EPs Kiss a Gun Down in October 1992 and Strange Brew in October 1993. After returning to Mental As Anything, they continued with their Dog Trumpet side project and provided three further album releases.  Mombassa also designed innumerable T-shirts, posters, videos and record covers for Mental As Anything and other bands. His most recent album cover is for Public Image Limited's "Greatest Hits So Far". Johnny Lydon spied Reg's work on Mambo clothing and sought him out to do their album cover. Reg's talents extend to illustrations and writings for, among others, Rolling Stone, Stiletto, RAM, Dolly and FMG.  In 1986 Plaza released a solo single, a cover of the 1960s Unit 4 + 2 song "Concrete and Clay", which was a No. 2 hit; the subsequent solo album, Plaza Suite, also charted. In 1991, during his sabbatical from Mental As Anything, Plaza collaborated with former member of Models, James Freud. As Beatfish, they released the self-titled album, Beatfish, which was one of the first Australian dance or house flavoured albums. Plaza's 1994 album Andy's Chest was composed almost entirely of Lou Reed covers. Another collaboration with Freud occurred in 1996 and resulted in the Hawaiian inspired Moondog project, with Plaza appearing on some tracks of the album Postcard from Hawaii.  Smith performed with his band, Greedy's on the Loose, during 1992 but there was no recorded output, while Twohill returned to art college and finished his degree. In 1996, Smith released his solo album, Love Harmonica, and toured with his band, Greedy's People, which re-recorded his solo album and released it as Greedy's People in 1997.  In 2006 Smith appeared on television gameshow You May be Right, hosted by Todd McKenney. The program pitches two teams of celebrities against each other as their knowledge of movies, music and television is put to the test in a series of fun trivia games.

Did they have other side projects?
After returning to Mental As Anything, they continued with their Dog Trumpet side project and provided three further album releases.