Tools to create mobile mockups

Hi guys, I need to write a RASD for my soft eng class and we also need to create some mockups for our app. Do you know any tool that will easily (and quickly) allow me to do that? I'm thinking of something like Visual Studio which lets design a desktop application by drag and drop, but for mobile apps. I don't need many components, only some images, text and some radiobutton, it need to look like a real app.

Thanks.