I think Ufasoft Coin does just the thing :
https://bitcointalk.org/index.php?topic=58821.0The GUI needs development and it's most likely missing features that are in the main client, but it's working.
These clients work by running the bitcoin/litecoin daemon separately and interfacing with it using JSON-RPC, so it could be possible to make some cool stuff, such as a client that starts up immediately, allowing you to look at your transactions and such while the daemon finishes loading up (actually, I think that's what etotheipi is working on his Armory client right now) or running multiple daemons with different wallets.