I simply love this thing. You may think: "Ok, a vocoder. What's new or surprising about that?" Yes, it is a vocoder with the ability to lock a scale but it is so much more: harmonizer, autotune-like pitch-shifter, 8-voice synth, multi-effect tool...you can even use it for vocal-to-midi like Dubler. Ovox is one of those plugins you should test on nearly every kind of sound. For e.g. it is amazing on drums. Just load it on your drumchannel and go through the many really cool presets. Try the demo, you will not regret it.
Sometimes you can get it on sale for $30, an absolute bargain!