Carbon offsetting

We're thinking of taking a summer holiday somewhere hot this year - maybe Italy, Bulgaria, Croatia or somewhere Mediterranean. We made a resolution a few years ago not to fly becuase of the huge contribution flying makes to climate change and all our holidays in that time have been in England, Ireland, Scotland or France where we can either drive and take the ferry, or go by train and ferry. (For our work my partner and I have sometimes had to fly in this time to attend meetings, conferences etc so we are still making our contribution to CC :-(

We've been thinking recently about carbon offsetting - where you buy something that offsets the greenhouse gases you produce from flying. If we do take the family on a flying holiday we would really like to do this but I'm not sure where to start. Does anyone have any knowledge of the different schemes? Or information about which are 'genuine' and how to tell that you are getting what you pay for? Have any of you done this before?