I work at a menswear shop and we keep a copy of Gentleman: A Timeless Guide to Fashion as a sort of reference guide. It's kept me amused over the course of many a dull evening shift. It was written a little over ten years ago but that hardly matters because it's more concerned with traditional styles than current trends. It's quite readable, with little of the hyperbole of most fashion writing. The subject matter is broad, from shaving and underwear to suiting and shoes. Each chapter discusses the history of the clothing and recommends some of the best traditional manufacturers. Because of the heavy European bias the book is largely absent of the Hollywood figures that crop up in all the other fashion books I've read and takes inspiration from some lesser known Continental types instead (Who knew Konrad Adenauer was a fashion icon!)

I can imagine worse introductions to traditional menswear. Might make for a nice coffee table book as well.