Easy & cheap way to book rental cars

Used RentalCars.com to book cars in several countries over the last 8 months and found it a simple and easy process.
It is easy to find the best deal available, including extras like second driver for free.
Had no problems at the respective rental companies when it came to picking up the booked vehicle, and with it being pre-paid avoids many hassles (just need to remember to allow for the bond to be put on hold on your credit card).
Last booking was for a car from London Heathrow over the Christmas period, for 3 weeks. Because it was pre-booked and pre-paid through RentalCars.com, the guy on the Budget Rentals desk was able to ensure I had a car with sufficient mileage left on the vehicle for the duration of my hire.
I also knew what to expect regarding Excesses on the insurance and knew what wasn't needed because it was already covered on my personal car insurance back home - or on my travel insurance.
The vehicle I ended up with was ideal for my requirements, very easy to drive and economical on fuel (helped also by falling fuel prices).
Appreciated the hint given at the time of picking up the car about returning it full - he even recommended the cheapest local garage to fill up from.