As far as I know, the alert key is the only special one with a public key hardcoded in the client.
Technically, the public key of the genesis block's output is also hardcoded in the client, but it grants no special privileges. The genesis block cannot even be spent.
As described in the Alerts article on the Bitcoin wiki:
Only alerts that are signed by a specific ECDSA public key are
considered valid. A copy of the private key is held by at least
Satoshi, Gavin, and theymos.
All alerts that have not expired are relayed but the client displays only the highest priority alert that hasn't yet expired and wasn't ...
Yes, according to Gavin Andresen via Reddit.
Even if they didn't to do so, Bitcoin Core already has two other mechanisms which will produce automated alerts as the hard fork approaches: one which will take effect before the hard fork occurs, and one after (as per BIP-50).
You can't. bitcoin-cli has never had the capability to send alerts. It is not possible for a user to push out an alert from any Bitcoin Core node.
Alerts were sent by using a specially modified version of Bitcoin Core which had the particular alert to be sent hard coded into it. Developers have to modify Bitcoin Core and include the alert code in a local ...
I have never used it personally, but I have a lot of good things of the Bitcoin Paranoid app. It's supposed to alert you on price changes.
Here's the bitcointalk thread: https://bitcointalk.org/index.php?topic=178391.0