Nevermind litecoin and dogecoin, they don't provide much of an improvement over the original protocol.
Check out mastercoin, counterparty or electrum, they propose some interesting ideas layered on top of bitcoin and that's what I'd love to see.
Did you mean ethereum? Ethereum isn't layered on top of Bitcoin. Mastercoin and Counterparty are both interesting additions but still need to prove themselves creating real economic value.