I found this picture depicting the relative sizes of objects in our solar system from a website called The Size of Our World. I think it is one of the best depictions of the relative sizes of the Sun and the planets. I plan on using ALL of the pictures from this website when we discuss planets and stars.
When I attend the Space Science Educator's Conference in February of this year I also learned of a unique way to present the sizes of the Earth and the Sun. The Earth is easy, you use a hole punched out of a piece of paper. The Sun will be a yellow cirlce 114cms in diameter.