Your Value Proposition as a Software Developer

Sometimes folks will tell you to think about your value proposition – what actual benefit you bring to the table – as a software developer. That could be to negotiate your salary, interviews or promotions. It could be as a freelancer or consultant. It could also just be a way to let you get included in a really cool project (“hey, I can help you out!”)
So what’s your value proposition? What do you actually bring to the table?