A Hierarchical Deterministic (HD) wallet has some nice features such as easier backup (instead of needing to backup multiple keystore files and the passwords for each of them).
Are there any implementations of an HD wallet for Ethereum?
This is a community wiki of HD wallet implementations for Ethereum.
I only know the mobile Jaxx app wallet for now that can handle Ethereum HD accounts all linked under a mnemonic. It can also handle bitcoin. It's my favorite wallet app for the moment if you only want to receive and send ether and not interact with contracts.
Note that Jaxx is still in beta, so use it with small amounts.
Bitcoin operates under a UTXO (unspent transaction output) system, which necessitates new addresses for each transaction. Ethereum, in contrast, operates on an account based system. While it would be possible to deterministically generate a tree of accounts from a single seed in Ethereum, there's really no need to, because a single account can handle all of your transactions.
If I understand that right, then you can create HD-wallet yourself using this tool by Ian Coleman.