National Strength and Conditioning Association (NSCA).
My friend works at Ballys in NY...they require NASM, but it was all online. I saw the online NASM test and didn't think it was that difficult. There was no charge as it was taken through the Ballys web site.
I spoke to Juan Carlos Santana, who is NASM certified, and asked him if he recommended it. He said he would go with NSCA if he had it to do over. My understanding is NSCA is the most "hands-on" or real world/sports cert out there. I'm considering it myself.