[drenkrom]

Melodyne goes way beyond retuning vocals and opens up great creative opportunities, so it gets top marks among the suggestions from me. It looks funky if you don't know it but the learning curve really isn't that steep if you're not allergic to reading. Autotune is pretty much a standard and works pretty well if the vocal is going to end up in a mix. Accapella, it can be heard working pretty clearly, no matter how finely you work it in graphical mode. Autotune lends itself perfectly to whacking out vocals Daft Punk-style, though. I don't know if that's worth anything to you, but it's essential to a lot of my work, personally. For pristine sound, I've heard a lot of good for Waves Tune, but I haven't logged enough time on it to pass a solid judgement. Same goes for the Serato stuff.