1. LA2A or Fairchild compressor, that is what they do best.
2. Parallel compression off the main vocal, that is what it was designed to do i.e. fatten things up.
3. Mix into a Neve 33609 followed by a Pultec on the master buss. Of course that will fatten the whole mix as well.

In the old days .... They used an aural exciter ....

One easy way to thicken vocals without actually doubling:

Put the Sonitus Modulator in the FX bin, set at a slow flange and set the mix to 10% wet (or start at 0 and increase until you can barely hear a difference).  It is subtle but effective.

Robby mentioned whisper tracks, here is Yep's vocal guide where he also discusses whisper tracks.
http://forum.cakewalk.com/tm.aspx?&m=830309

My singer is a Japanese girl, and I have record my voice as a whisper track behind her! (don't tell).

best vocal sound for a "single track"  that i've achieved is with a portico set on "silk"  with the uad la2 and uad fairchild.   man that sounds good... of coarse that's also using a  u87 as well.  but one track super thick and warm... just added a tiny bit of uad's plate 140 and viola... easiest vocal sound i ever got.  every one asked who i had singing the track?  it was me and i'm definently not a seasoned singer...  it was just a trial of the new portico and uad stuff.  definently will be my go to line for vocals from now on...  or should i say for now.

word

smoochy


best vocal sound for a "single track"  that i've achieved is with a portico set on "silk"  with the uad la2 and uad fairchild.   man that sounds good... of coarse that's also using a  u87 as well.  but one track super thick and warm... just added a tiny bit of uad's plate 140 and viola... easiest vocal sound i ever got.  every one asked who i had singing the track?  it was me and i'm definently not a seasoned singer...  it was just a trial of the new portico and uad stuff.  definently will be my go to line for vocals from now on...  or should i say for now.

I have used that exact chain, and it is nice. So pleasing to the ear that it makes an out of tune performance irrelevent. I like when that happens.

one thing i forgot to mention... the portico burned up on re entry.  about five minutes after finishing the track.  the teks can't seem to give me a reason for that.... kind of scary.  but man it sounds so good. i actually overlooked it's shortcoming.  so far the new one has been stable. 

I'm a newbie and this is very helpful. Thank you guys.

http://www.soundclick.com/rossbrigoli

i'm old school about these types of things.

nothing sounds as good to me, as hearing something sung twice, exceptionally well, and mixed together.


that is the holy grail of thick vocals.

is it easy?
hell no!


if it was, everybody would have killer thick vocals.