Corsair and OCZ are some of the best brand you can get right now. Rizinc, if you look closely at your RAM stick, you'll be surprised at the fact that most of the actual chips on there are made by samsung regardless if the actual stick is made by corsair, kingston whoever....but generally Samsungs name is on the actual RAM Chips...also I have a stick of samsung and it's simple valueRAM and overclocks pretty good. It can OC from PC2700 up to PC3200 so with those couple factors in mind I believe Samsung makes some pretty good RAM.
But as far as people looking for the best and top quality RAM manufacturers, most will agree, corsair, OCZ, mushkin, are top brands.