Living in London is great except for if you own a car. Admittedly I ride a (motor) bike most times but a car is an necessity for transporting luggage, computers, friends and, err... the lady (esp when dressed up). Also admittedly my annual car mileage is low, prob a few thousand if that. So for the past several years I've used Zipcars for short journeys (up to 60 miles before incurring mileage charges), includes fuel, Congestion Charge and insurance. £15 per month, first 3 hours in a month included, then an hourly charge (starting at about £6.50)
Longer hires or journeys I can rent a car from Hertz for as little as £20 per day, unlimited mileage. Now I know the guys at the local rental they usually upgrade me to a much better one than I've booked!
I don't think I've had any car older than 2 years or more mileage than 11,000. And they're always clean...
Can't beat walking away from one and forgetting about it!