Professor Ann Curzan, the scholar on the history of English we interviewed for last week's Behind The Dictionary feature, recommends these books on the subject:
David Crystal's The Stories of English "is packed with interesting information about the history of English."
Bill Bryson's The Mother Tongue "is a very accessible history of English."
John McWhorter's Word on the Street: Debunking the Myth of "Pure" Standard English "is also accessible and treats both language change and dialectal differences."
Language Myths, edited by Laurie Bauer and Peter Trudgill, "is a collection of short, very smart essays that address a range of myths about language -- language change, dialects, the effects of TV, etc."
"Michael Adams and I have written an introductory textbook about English linguistics that people tell us doesn't read like your average textbook (which was absolutely our goal!): How English Works