With the holidays, I had some free time to hack and made a new site:
http://coinspy.ioYou can "follow" any number of addresses. The system watches network and as soon as a transaction gets broadcast, you'll get an email with the details. The emails come pretty fast, normally within a few seconds. You can follow "famous" addresses like the silk road address and find out if and when the FBI will do anything with the BTC. Or you can just follow the public addresses of your cold/offline storage and get alerted in case the private keys are compromised or somehow used (this is why I created it for myself).
Anyway, I would love to hear feedback and get some ideas as to how to improve CoinSpy.