You do not specify if you are looking for hand quilting thread or machine quilting thread. Also many people refer to thread as "quilting" thread when they really want thread for piecing. Anyway, here are a bunch of good sources for thread and superior threads has tons of good free info on what threads are best for what job.
http://www.superiorthreads.com/
http://www.redrockthreads.com/
I really like Isacord embroidery thread for machine quilting and I have ordered from these guys.
http://www.sewforless.com/category/1...ord_Thread/c88
My favorite hand quilting thread is Valdani. My LQS carries it but I did find this on line source
http://www.thethreadexchange.com/miv...FcG77QodL3bFBA