If it hasn't been very long, but still long enough for them to get some space and perspective, then I second scott_s' advice. They might feel the same way, and

If it hasn't been very long, but still long enough for them to get some space and perspective, then I second scott_s' advice. They might feel the same way, and you might come back together stronger than you were before. If it's been too long, I think it's still worth a shot, but you're more likely to have a cordial but somewhat distant relationship rather than a return to best-friendship.