NO EXTERNAL DVD-R WORKS WITH iDVD.
Otherwise you may want to look at either the EZ-Quest (two versions - one with software and one without) or the Lacie (I believe it comes with their own DVD software). If you are going to use DVD Studio Pro and Toast then it really doesn't matter. Nearly all use the same Pioneer DVD burner that Apple uses. Just make sure it's a 4x burner.
The $380 price range is right around how much they all cost. I have seen the EZ Quest for $350.