I agree with the previous posters: "scrappy" covers a wide range of territory. I call the "throw everything together" a "kitchen sink scrappy" and in my opinion Postage Stamp or String Quilts are perfect examples. Or you can go more controlled. One method I have found very effective is the monochromatic scrappy, where I use just one main color, expressed with many different fabrics. My "Green" quilt is an example of this.
Another technique is to take a regular pattern but substitute certain parts of the pattern with scraps. Bonnie Hunter is a master of this; many of her quilts utilize this technique. I have a wall hanging where the flowers are single colors but the background is a collage of squares and rectangles of every cream and beige I had at the time. My machine quilter really brought the quilt alive by quilting dragonflies, bees and butterflies in amongst the flowers and it's one of my favorite quilts to this day.