rumleymusic
We should clarify that stereo wideners do not work on mono sources.  There are effects that can create a stereo effect from a mono signal.  Waves has one, PS22, Bob Katz made one, and Brainworks has one that I like to use on occasion when I cannot mic an instrument in stereo.  
 
Other than that, a short room or reverb send can create the openness lost in a dry mono mic recording.  

You can also do it yourself with two sends with delays and some very gentle chorus. If you can hear the chorus, it's set too high. Pan each send hard right and left, put slightly different but very short delays on each and add a little chorus to give it a tiny bit of motion. From the 80's...
 
There is a youtube video that demonstrates the setup. It's very easy and very flexible.
 
Regards,
Dan

I am a fan of Audio Damage's 'Discord' plugin, which is a pitch-shifting delay w/ lots of bells and whistles. It's got a few different algorithms, and some nice modulation controls, as well as feedback, and per-channel delay controls. Pretty capable little plug, and easy on the wallet.
 
http://www.audiodamage.com/effects/product.php?pid=AD025
 
FYI, I have no affiliation with this company. I just think they make great stuff that doesn't break the bank.

greg54
As for vocals (and even guitar), you can always convert them to stereo.  
 
Thanks!
Greg

Hi Greg,
 
Just to let you know, the above is not really true and I'll explain why just for your head. :)
 
When you have a mono signal, it is always a mono signal. Converting it to stereo just doubles the mono source, brother. For example, say we take an output from a guitar processor like a POD. One output of a distorted guitar sound, is mono.
 
Now lets say we take two outputs from that POD and we have a chorus effect on the guitar. The guitar sound itself is STILL mono. The chorus gave you stereo imaging, not true stereo.
 
Remember, just because you see two wave forms in a single file doesn't mean stereo. Also, there is no need to turn a mono file into stereo in SONAR. The reasons being...
 
a) the file remains in mono no matter what as I mentioned above
b) SONAR has the ability to take a stereo effect and put it on a mono track giving you a stereo imaged sound.
 
The effect is what gives you the stereo sound. Real stereo entails two separate signals that are independent. For example, let's go back to our POD with the distorted guitar...
 
We take that single output and record the mono track. Then, we hit rewind, create another track and play the exact same thing. Pan the first one left, the new one right. NOW you have true stereo. What makes it stereo? Your human timing inconsistencies with stops and starts, different ways of executing the same chord passages, chord inversions and the coolest...two different eq curves.
 
Now, keeping all this in mind....I also wanted to touch a bit on what Daniel said. When he mentions wideners not working in mono, that is correct. However, if you have a stereo effect on a mono signal, the widener/stereo enhancement plug will work as it should. You just can't put a Waves S-1 or the Sonitus Phase plug on a mono signal that doesn't at least have stereo imaging due to the effects that MUST COME BEFORE the widener is inserted. Hope this helps a bit. If you knew all this already, my apologies....I just wanted to make sure. :)
 
-Danny

greg54
Hi Danny -
 
Sonar allows you to "convert to stereo" a mono track.  That was all I was referring to.  And no, I did not know everything you just said.   I appreciate the explanation.    :)
 
Thanks!
Greg

Hi Greg,
 
Yep I hear ya. I just wanted to explain that even though sonar is claiming stereo, it's just creating a dual mono file within the same track. Glad I didn't waste your time with that post. :)
 
-Danny