What is the best way to create a vocal double using the same single original vocal take, without actually recording the take again? Using a chorus effect maybe? Manipulating a second instance of the same take some other way? How do you do it?

I want to create a subtle double during the chorus of my song using the same take as the original, and was wondering what your ideas are.

Thanks!

P.S. Please do not tell me to just record another take. I know that is the best way. But for my purposes, I want to know how to use the same take to achieve this.

Avox-duo

If you have a delay that features random modulation, use that on the clone with a short delay (5-10ms) and 100% effect. Detune the clone sharp by 5-7%, then make a second clone and detune it flat by the same amount.

Very nifty trick bitfipper !
I'm off to give it a try, thanks for that.

I find this quite useful...

http://www.g200kg.com/en/software/kerovee.html

V-Vocal with very slight formant change, then delay or advance one vocal somewhere between 15-30ms.

X1 producer has the VX64 vocal channel that has a doubler. 
  
Plug ins include A.D.T. (by Olaf Matthes), which I think is free, and Martin Eastwood Audio Duo, which may be free, I can't remember.  These two plugs let you vary lots of parameters, and are quite effective.  I used to use A.D.T. a lot, but then started using Duo (or is it Duet? I'm not at my DAW.) 

Sound on Sound has a good article on Vocal Production which includes a number of ways using subtle time shift, pitch shifting etc. for fake double tracking.
http://www.soundonsound.com/sos/feb12/articles/vocal-production.htm
 
You can use V-Vocal, too: apply it to a clone of the original and combine modified and un-modified versions;
Subtlety seemes to be the key word.
 

Dave Pensado (very well known mixer, if you aren't aware) did a video on how he achieves this.

http://www.youtube.com/watch?v=IyHKZtCbbks

I personally avoid doing this at all costs and go with a second tracked vocal, but if that ain't an option - the above could help.

You surely will find the same phrase sung in a different place of the same take. The chorus, for example.
 
Find them and use those.

Doubling a whole song gets boring, so let serendipidy dictate which bits get doubled.