My mom used to work for Zales about 25 or so years ago (before they turned into the mall-junk they are now) and had a great time there, but times have changed. For the most part, Zales has a very limited stock on hand and typically uses the lesser certifications (EGL, IGI, etc.). The quality of their stones and jewelery is sub-par for the price, and the service typically stinks.
I'd advise looking elsewhere, privately owned jewelery stores are the way to go. Look for places that have the majority (if not all of their stones) GIA certified, AGS would be another good certification to look towards as well.
Also, check out the forums at
PriceScope.com They have a lot of extremely experienced jewelers and gemologists that can give you more advice.