SpareKeys.com

Excellent idea here. SpareKeys is a company that holds a set of keys on your behalf so if you ever lose your house keys or even if you wish to leave a set for visitors to use your house whilst you’re away, you can do so in safety. The odd thing is that their main security feature is that they never know your address – they won’t deliver your keys to within 100 metres of your house and you don’t even need to enter your address for payment.
Shame it’s so London-centric.