What is a proof of stake coin? It is a type of cryptocoin that, if you hold enough of them in your own wallet for a specific amount of time, you will be rewarded with additional coins. It is not enough to have them in an exchange site, you actually need to have a wallet for said coin on your computer, and it often needs to be unlocked in order to stake. Think of staking as a form of mining, but without the need for special hardware or any of the elevated electricity costs and such. The only downside is that if you have less than several thousand coins the staking process can take a long time.
808 Coin
808 Coin (808) is a POS (proof of stake) coin. They mature after 8 days, which is when you are expected to "unlock" the wallet (in order for it to engage in the staking process). The name of this coin comes from the 808 Roland mixer that was originally built back in the early 1980s. Currently, this coin gives a 808% return yearly. That is 17% or so every 8.08 days (eight days and a few hours).
For the most up to date information, the best place is 808 Coin BitcoinTalk Thread
HoboNickels
HoboNickels (HBN) is a Proof of Stake coin that was created on September, 2013. It earns you around 2% every 10 days. For more info about this coin, their BitcoinTalk is an excellent place.