The RAM industry has its own cast of manufacturing characters, some of which you've heard of (Mitsubishi, IBM) and some of which you haven't (Eurotechnique, Zilog). OS X's System Profiler app will give you the manufacturer code for your RAM DIMMs; see if you can match the last two digits against the Hex column in this PDF list.
My computer's RAM was built by Micron Technology, a company with a high-tech name so awesomely generic it sounds like it should be the corporation that the villain runs in a early '90s techno-thriller. Micron's original manufacturing facility is located in Boise and that may be where my RAM was manufactured. However, in the last several years the company has expanded its production to Japan and Singapore.