In continuation of the last few posts by Litotes about coins that are not round,
The Indian Rs.2 coin is 11 sided(although it looks almost round). Production of this was stopped about 5-6 years ago, but many of them are still found in circulation.
Several older(late 1960s to early 1990s) Indian coins were not round.
In order: 1paise(1p)-square/diamond, 2p-sine wave on a circle, 3p-hexagonal, 5p-square/diamond, 10p-sine wave on a circle(looks almost octagonal from behind), 20p-hexagonal