This influential and widely used book has been extensively revised and includes a new chapter on linguistic discrimination on the basis of class, race and ethnicity.
Sensible overview of topics in sociolinguistics, with an enjoyable account of prescriptivism and the "complaint tradition". Bonus: Chapter 2 alerted me to an absurdly cranky essay on malapropisms (broadly understood) by Kingsley Amis ("Getting It Wrong", 1980) that compares "floating hopefully" to Japanese cars as "the most widely and loudly denounced import to the U.K.", and suggests adding the following usage label to the dictionary to supplement joc. (jocular) and vulg. (vulgar): "illit. (illiterate)" (33).
I like their (this book is actually by two authors, James and Lesley Milroy) explanation of standard language as an ideology which via pre/proscription suppresses what would otherwise be equally acceptable variations.
I need to read more of this, though, and maybe Trudgill's edited volume on standard English too.