Catalogue des idées reçues sur la langue - Marina Yaguello
A thoroughly excellent book of popularization: small, friendly, clear, covering just about all the concerns that tend to come up in common thinking about language, and giving a good idea of what linguists actually do (although barely mentioning such issues as syntactic structures and theoretical debates). Some of the idées reçues which Yaguello (a linguist) discusses are specifically French (does anyone actually imagine that Blacks are "genetically incapable" of pronouncing the sound R?) but most apply to English speakers as well. She covers things which people discuss, and also some that wouldn't occur to them but they need to know about: issues such as is language logical, are some languages more logical than others, is there a hierarchy of complexity among languages, how many languages are there, how different are they; discussions of norms, prescriptivism, written and spoken forms, dialects, national status, social stigmatization, relationship of language and thought (a short and sensible treatment), bilingualism; "it's not a word if it's not in the dictionary"; and more.

I wish I knew of something equivalent in English -- I'd buy a couple dozen copies and go around handing them out.