Log In Is a great site. You can send cards to the UK from anywhere in the world for £1.99, including first class postage, which makes it around £1 cheaper than Moon Pig and Funky Pigeon. The interface is really easy to use, even for those whose computer skills are minimal, and there's a great choice of cards for all occasions. We divide our time between Spain and the UK, so if there are birthdays on the horizon while we're away, I just log onto Personalised Cards.
Is there anything else that is totally free? You know, the way ecards used to be at first... for those who remember