I have a couple fillets that are not as nice as I had hoped and have been slaving away with sandpaper on a dowel. They are coming along OK, but then I remembered the set of cabinet scrapers I purchased from CLC. The french-curve shape one is ideal for this purpose. I am extremely happy with the results and it goes pretty fast. I even decided to improve a bit on one that was nice but not quite up to par.
Try this, I think you'll be pleasantly surprised (but wear gloves--those things are sharp!).