A recent Kosherblog post by Jabbett discussed the ethics of kashrut agencies certifying products that do not actually require rabbinic supervision. The post focuses on rubbing alcohol, which clearly does not require certification, as it is inedible (and also toxic). However, there are many edible products that do not require certification, either -- some less intiuitive than others. It is mainly due to ignorance that the very observant (even many rabbis) tend to insist that all processed foods be certified kosher.
This ignorance is fully understandable. Distinguishing between products that require rabbinic supervision and products that do not requires thorough knowledge of both the laws of kashrut and modern food processing techniques, and the latter may change at any time. In the age of the Internet, however, there is no reason why the kosher-keeping public should not be kept up-to-date on such matters. So I was happy to discover this site, via a comment by Jabbett on his own post. Rav Eidlitz is a renowned authority in the area of kashrut and is not affiliated with any particular certifying agency. His site contains a great deal of valuable information on keeping kosher, including a list of products that do not require rabbinic supervision. Here are a few that may surprise some readers:
Coconut Milk (not from China)
Corn (plain and cream style - frozen or canned)
Rice Pasta (containing only rice flour and water)
There are certainly some things on Rav Eidlitz's site that are debatable, but for basic information on kosher products, it's a great placed to start. (While you're there, you should read the Kosher Alerts, although they are sometimes upsetting.)
Oh, and stay tuned: Jabbett is planning to post a more comprehensive list at Kosherblog.
UPDATE: DH says that he has known about this site for "a long time." Thanks for telling me! (J/K)