This was about 10 years ago.
The naive answer I would have given at time was: "I'm a software developer who builds ecommerce and CMS sites."
And it's funny that you ask "What do you do?" At the time I had starting taking on projects from a friend who had been doing development contracting for about 4 years. One time when a client told me my proposal was priced too low and passed on my bid I was baffled.
I told my friend about it and he asked me the same question, and I gave the above answer more or less. He corrected me and said "No! You're businessman enabling a national sales channel for a local or regional business who wants to increase their revenue."
So never define your price by what you do, rather define it by what the value of thing is you're delivering to the client. This requires some research on your clients and a realignment of your thinking. When you're contracting as a developer, you have to start considering yourself as becoming a successful businessperson and not (just) a successful software engineer.