Harmonizer from 7 aliens is an awesome plug. It is a midi harmonizer.  (Vielklang is an audio harmonizer I think ??)
 
When I went 64 bit Sonar, Harmonizer went bye bye.   Would not work with any wrapper.  Interestingly, other DAWs were able to wrap the 32 bit version, but Sonar did not.
 
The developer updated Catanya to 64 bit recently and that works in Sonar (mostly...but lets not get Silk Tone started....) .  Hopefully he will update harmonizer soon.  (he replied to one of my e-mails that he was working on it)
 
Vielklang is a weird one, I bought it and never quite got it to work well.  Sounds like if I invested some time to figure it out it might be useful.
 
JR

yeah i thought the op asked about midi plugs (hence kirnu) but everyone else seemed to think otherwise?

Vilelklang Just released a version 2 which is a lot more user friendly. It is audio and midi. You drag a clip into the vielklang interface and control the harmonies in real time via midi.  There severeal different ways to generate harmonies with this plugin and it sounds good and easy to use.