Blockchain.info has some really nifty(and free) API methods.
When a payment is received blockchain.info will notify the http URL specified in [Account Settings]. The parameters will be supplied in a http GET request. The callback url is limited to 255 characters in length.
Parameters
value The value of the payment received in satoshi (not including fees). Divide by 100000000 to get the value in BTC.
transaction_hash The transaction hash.
input_address The bitcoin address that received the transaction.
confirmations The number of confirmations of this transaction.
{Custom Parameters} Any parameters included in the callback URL will be past back to the callback URL in the notification.
Yeah unfortunately i need to pay for a special VM just for the wallet that way. That and the JSON RPC api didn't look all that simple. In a way coinbase does exactly what i need, except its callbacks don't work. It would be nice to be able to fire up a super secure wallet VM with a locked down webservice api for adding receive addresses and getting callbacks, and having a 2 factor 'withdraw' function.