I'm recording my album (rap) right now and in a few cases on choruses of songs, I have 2 or more layers and would like to be able to pan some to the right and others to the left. However, when I run the tracks through a stereo bus with reverb this seems to basically negate the pan. What is the best way to accomplish what I'm trying? Do I need separate mono buses and pan the bus itself? I would like to minimize the number of buses for the sake of resources, so using a single stereo bus would be ideal if it's possible. Thanks for any suggestions.

Strange. According to my understanding the stereo bus should maintain the panning of incoming mono-tracks. Maybe I'm wrong then. IIRC I've often used stereo buses for panned mono tracks of diffrent kind, guitars, backround vocals etc., with success.  Could the reverb used be the culprit? What happens without the reverb?

  You may need a mono reverb and use it directly on the tracks FX bin. 

It sounds like you're routing the track output to a bus that has a reverb and then to the Master.  If the reverb has (or is set to) a mono input then you'll loose all your panning.

The "correct" way to add reverb (there are many preffered methods) is to route the vocal track out to the Master bus (or vox sub-bus if you're using them), place a reverb in the FX bin on its own bus and assign a 'send' on the vox track to the reverb bus.  Turn off the DRY signal in the reverb so the only output from the reverb bus is reverb...

However, when I run the tracks through a stereo bus with reverb this seems to basically negate the pan.

Sounds like you're using a reverb plugin that isn't True Stereo.
Pan position is kept intact when routing to a stereo bus.
Otherwise, you wouldn't be able to preserve the stereo image of a mic'd drum-kit, etc.

In "true stereo" reverb, each channel (left and right) is processed separately... and each results in a stereo signal (ultimately summed together).  This preserves the original pan position of the source signal.

In a "stereo" reverb, the incoming signals (left and right) are summed to mono... and that signal is processed resulting in stereo ambience.  This is why you're losing the original pan position of the source.

Stereo reverb is used to conserve resources.  With mono sources, it works fine.  Only a problem when you have a stereo source where you want to maintain the original pan position within the ambiance.  

Some links on the subject that are interesting to read:

http://www.liquidsonics.com/software_reverberate_true_stereo.htm

http://forum.cockos.com/showthread.php?t=67620

http://www.gearslutz.com/board/so-much-gear-so-little-time/44989-fx-rundown-list-true-stereo-not-worth-spending-extra-cable.html

You would pan the send and the track the smae way. This also depends on the effect that is on the bus also.

Thanks for all the feedback. I figured out how to fix it though I still don't quite understand. After several of you mentioned the reverb I remembered I probably had used the mono version (Waves Trueverb), and I had. But even when I disabled, then deleted the reverb from the bus, the bus was still playing the panned track as if it was mono, so it was equal on L & R. I put a new stereo bus in though and problem solved, then used stereo version of the reverb. All good now. What I don't understand is, it seems like having a mono effect on the bus somehow converted it to a mono bus permanently, which seems kind of strange, almost like a glitch. At least I know now, thanks for the suggestions.

it must be a mono plugin