Synchro Arts Revoice Pro - it is simply the most amazing plug-in. It saves me hours of time (for example: time-aligning 3-part vocal harmonies, each part being double-tracked). It is like alien technology, or magic.
More unsung than the time-aligning function is Revoice Pro’s tuning. I think it is as good as, probably better than, VariAudio in terms of sound quality. It also has some cool tools line the one that lets you draw in the pitch tracing.
It is expensive, but I think it is the best DAW money I’ve spent.