Dan and Megan's Broccoli Salad

1 large head of broccoli - cut in small pieces
1/2 pound bacon - crumbled
1/2 cup seedless red grapes - cut in half
1/2 small red onion, chopped

Dressing:
1 cup mayonnaise
1/2 cup sugar
1 Tablespoon vinegar
1/2 cup sunflower seeds