Place bacon in a large, deep skillet. Cook over medium high heat until evenly brown. Drain, crumble and set aside.
In a medium bowl, combine the broccoli, onion and raisins. In a small bowl, whisk together the vinegar, sugar and mayonnaise. Pour over broccoli mixture, and toss until well mixed. Refrigerate for at least two hours.
Before serving, toss salad with crumbled bacon and sunflower seeds.