Huh? Bitcoin-qt has had *coin-control* for a long time now.
Ok it has, just had to enable it. Anyway, I did not immediately see a possibility to permanently lock some address so that its funds would never be consumed by any transaction.
Anyway - you can use pywallet to delete keys from your wallet (take a backup of your wallet first of course).
That's what I feared. At least an RPC call should be available for deleting a private keys.