Many companies make good relaxer kits including Organic Root Stimulator, Mizani, Profectiv, and Dr. Miracle. These relaxer kits, if used correctly, will encourage the hair to be healthy and strong.
No-lye relaxers by Profectiv and Phytospecific are both made with high quality ingredients and produce good results. For lye relaxers, Mizani is a favorite!
There are quite a few companies who make reliable kits for hair relaxing. Silk Elements, Luster, and African Pride and Motions are 4 of the main brands.
The best relaxer can be found at any professional salon. It is always best to have something like a relaxer done by a professional that way you know its been done right. Professionals know what to look for and what relaxer would be best for your hair. Never try to do such an complex "procedure" unless you already have experience.