First marathon inspirations: John Bingham aka the Penguin is a great guy to get you round your first marathon. Here's some of his best words:

"The finish line is not the end. The finish line is the beginning. Standing at the starting line gives you permission to hope. Taking the time to train, putting in the mileage, making the changes in your life, and taking the risks has given you consent to hope for the best in yourself. The miracle is not that you finished, but that you had the courage to start.

Crossing the starting line also gives you permission to dream. You can dream about the perfect day, the perfect race, and the perfect experience. It may not happen that way, but it doesn’t mean you shouldn’t dream about it. Crossing the starting line may be an act of courage, but crossing the finish line is an act of faith. And faith is one of the most powerful emotions you can experience.

Faith is what keeps us going when nothing else will. Faith is the emotion that conquers fear. Faith is the emotion that will give you victory over your past, the demons in your soul, and all of those voices that tell you what you can and cannot do and can and cannot be.
If standing at the starting line gives you permission to dream, crossing the finish line gives you permission to plan. Crossing the finish line gives you permission to plan for your next success, to plan for the realization of your next dream. The last step of the race is the first step of the rest of your life.

What you do now is up to you. You’ve seen what you can do. If you’ve stuck with the training program, you’ve seen yourself filled with joy and blinded by frustration. You’ve overcome your fears. You’ve been humbled by both the strength and fragility of your body. You’ve found what you thought were your limits and gone beyond them.

You’ve also learned that what stops most of us from achieving our dreams as athletes and as people are the confines of our imaginations. We can never be more than we imagine we can be. And as long as we restrict ourselves by our imaginations, we forever bind ourselves to our past and blind ourselves to our futures.

Your limits lie behind you now. With that one final step across the finish line, you liberated yourself from everything you ever thought you knew about yourself. You have taken the very first step on the course to your destiny."

Do it for a reason: Raising money for charity is also a great way to inspire you through training and get you to the start line. I think the best way is to organise the event yourself (flights, hotel etc) and then contact a charity. That way you have no minimum fundraising target to contend with as well as your training, and you are reducing spend on your charity for the money. I like to ask charities where the money (how much is unrestricted), what their fundraising ratio is and how I can see their charity at work. It's amazing how many big charities don't stay in contact with you after you fundraise. So far I've raised money at marathons for the Institute of Cancer Research and East London Community Foundation. Cancer Research UK didn't want to answer my emails.