I have reasonable luck creating a choir with my own voice on multiple vocal tracks with a little help from Voice Live by TC Helicon's octave doubler to crank up my voice up or down an octave in some parts.

I've been experimenting with changing the eq, adding vibrato, changing the pitch a couple of cents, and adding chorus and flanging effects to give each voice some variation.

I have gotten the best results with the mic at close range (12 - 18 inches) rather than from a few feet away (which is usually the choir mic configuration).

I'm open to any suggestions. Here's a sample in the first song "Whosoever". .
http://www.reverbnation.com/dmmnola