Every country in the world has its own monetary system, and they each have their own coins. Adding coins from all over the world to your coin collection will add diversity and interest to the collection. Imagine coins from North America, Africa, Japan, New Zealand and Russia. The possibilities are almost infinite.
Take a look at Africa. Each country in Africa is home to its own culture, and the coins from those countries offer a small part of those cultures. Like many other countries, coins that are from earlier times that are no longer used are more valuable. An example would be the South African pound (they use the rand now). The South African coins were available in 1, 3 and 6 pence, 1, 2, 2.5 and 5 shillings and and and 1 pound. All were originally made from silver, but beginning in 1932, some were made in gold. The Gold Krugerrand of South Africa is a highly collectible coin, and was first minted in 1967 to help the South African gold market.
Japan and China have also contributed much to the world of coin collecting. The coins of both countries are different from most coins and are very beautiful. Chinese coins were made by casting rather than being cut by dies like most coins. This makes them very unique. The majority of Chinese coins were circular with a square hole in the middle and decorated with Chinese letters and pictures. The Japanese made similar coins a long time ago, and made them from iron, copper, silver and gold depending on how much the coin was worth. The Japanese put the hole in the center so the coins could be easily charged on a string.
While not as old as other coins in the world, Australian coins were first minted in 1910. Oceanic coins were also considered legal tender in Australia for a long time, and they had an exchange value that worked with the prevailing monetary system. Australia also recognized the Spanish dollar, the English shilling, the Pagoda and the Rupee until 1825, when British currency became the legal monetary system of Australia.
Coins from Greece, New Zealand, Central America and North America are all different and unique. Each country has their own monetary systems that represent different cultures. Canadian coins like the Maple Leaf Gold coin are terrific additions to any world coin collection. Canadian coins all represent some small part of Canada on them. Mexican coins are also very unique since they have portraits of Mexico's leaders and culture changes from its history.
Adding coins from all over the world to your collection is a great way to learn something new about a different culture. Coins depict leaders, art and history of their countries, which makes each one valuable for many reasons along the obvious.