The CES is a great industry standard. The trainers that work in our department have seen increased skill as a result of that certification. Upon completion they all saw increase in revenue as they gained the ability to work more specialized populations.
Again this cert is very mainstream as more Trainers try to move into pre and post rehab and become more niche specific.
ACSM has a great cert as well, but the prerequisite are more intense.
There are also a lot of other one like Cook, Postural Institute, etc.
I would also look at Foundationtraining.com
Hope this helps,