There are some great cryptocurrency coins out there nowadays and the list continues to grow :D
My favourite is Monero which has an inflationary model, where once it reaches capacity from mining, it produces a steady rate of coins ad infinitum.
Nxt is a proof of stake coin, but being a coin is only the start. Nxt can act as a deed to property, work as a peer to peer file sharing system, be the basis for other coins to be created by users for their own application, and so much more.
Etherium is another interesting cryptocurrency. It is designed to act as a decentralized distributed contract system as well as a currency.
If you know about any interesting cryptocurrencies comment below!