I am sure it has already been mentioned, but I would like to talk about a little about Mastercoin. Mastercoin isn't strictly an alt-currency, rather it a protocol layer on top of Bitcoin; Mastercoins transactions are made on the Bitcoin blockchain. Mastercoin is still in its early stages of development, but among its goals are to create a fully-functioning distributed exchange, and a system of financial instruments, including derivatives contracts, currency pegs, "savings wallets", virtual assets. Currently, a Mastercoin is identified as such by sending a trivial amount of Bitcoin to a certain Bitcoin address, the "Exodus Address". Data is further encoded within the address to include the type of transaction and the amount of Mastercoin that are being sent.

Mastercoin's development is moving fast, and many people are already quite excited about it. If successful, Mastercoin will add an entire other dimension to Bitcoin, and will greatly increase the value of the latter thereby.