I'm trying to fade to black at the end of a clip (there's nothing after it). Right now, I'm using the "Fade through black", but after it fades to black, it fades right back into the video that just faded out before disappearing altogether.
Move your cursor up to the top of the timeline at the very end of the clip and you'll see a quarter circle and a two sided arrow. Hold down your left mouse and drag left to slowly fade to black. The further you drag, the longer the effect takes. Doing the reverse at the front of the clip increases opacity. If you don't like the default settings, right click, and pick another.