Agreement form for clients.

Hi! I just started on my web "consultant" venture and am doing part time web work for companies that need help. I don't know how to explain what I'm looking for but I will give a scenario.

A company hires me to re-design their company website. I would tell them that I will make 2 layouts for them, from which they will choose which layout to go with. I will charge a flat fee for the two layouts.

Here is my problem, I just can't tell them I expect to be paid this much, I need a legally binding agreement that they will pay me for my work. Where can I find such templates for a document like that?

Thanks
-Ty