Australia sports a twenty cent piece.
Diameter: 28.52 mm
Width: 2.5 mm
Weight: 11.30 g
75% copper, 25% nickel
First Mint: 1966 - current
Australian Decimal Currency
The twenty cent coin usually has one of three portraits of Queen Elizabeth II on the obverse and a platypus on the reverse.
There have been occasional commemorative coins over the years but the 1966 platypus design is still used on current coins.
The twenty cent coin was originally handy for drink machines and parking meters, but prices have shifted. You're now likely to spend some of the gold $1 or $2 coins as well.
Wikipedia has a great page with all the finer details for currency geeks:
http://en.wikipedia.org/wiki/Australian_20_cent_coin