Real Simple posted an article with eight simple flower arrangement ideas. The main tip is to use a unique container with one or two different types of flowers. My favorite from their bunch is the gerber daisy table runner with wheat grass - very simple and summery. Click here for step-by-step instructions.
I also like the idea of using beach pales or terra cotta planters as containers too. These are things you have lying around the house - why not put flowers into them to give them new life! Click here for some more ideas.