Websites
While not all these sites align with my approach to teaching about language variation, they all provide useful information for teachers hoping to learn more about how language actually works in the world.  The main take-away is that Standardized English is just one variety of English nestled among many overlapping varieties. The more we can describe how languages actually work, instead of prescribing how English should work, the more useful our Language Arts teaching will be for our students.

American English: Dialects and Variation
The companion website to the 2015 book with the same name, the linked appendix provides an extensive, meticulously researched, listing of features of English dialects.  If you're wondering how to describe any unfamiliar language forms your students might use, this is a great place to find it.

Voices of North Carolina Dialect Awareness Curriculum
The North Carolina State University linguistics department has created an entire curriculum on dialect awareness.  All the materials, including background information for teachers, is free to download.

The Ling Space
"An education project whose mission is to help make linguistics more accessible and fun." They do a great job.  There are a range of YouTube videos arranged by topic.  For the purpose of English teachers, I recommend starting with the Sociolinguistics section and working out from there. You can also find interviews with some of the other linguists and educators whose work I recommend.

Valuable Voices
Dr. Anne Charity Hudley and Dr. Christine Mallinson have put together a comprehensive set of resources for educators on teaching about language variation.

Do You Speak American - What Speech Do We Like Best?
From the PBS series "Do You Speak American?" this website contains a variety of information about language prestige and prejudice.

Yale Grammatical Diversity Project
The Yale University linguistics program curates a growing site intended to inform and inspire people to learn about differences in grammatical constructions in American English.  Students will likely find some familiar phrases and some brand new ones.  Great for exploration that validates language variation.

Dictionary of American Regional English
The University of Wisconsin hosts an online dictionary based on regional vocabulary.  There are interactive maps as well as a simple search bar.  In addition to definitions of regional words, the sight also includes audio recordings.  If the dictionary isn't enough for you, information about the entire project can be found here. 

New York Times dialect quiz
Complete this survey to find out what part of the US your dialect comes from.  After each question the site provides you a map of the US showing where the varieties of a word or phrase are most common.  A more extensive version of this quiz can be found at The Cambridge Online Survey of World Englishes.

North American English Dialects
Rick Aschmann put together an extensive dialect map of North America.  The page is a bit crowded and dense, but its worth spending some time sorting through.  People with some linguistic background can get lost for days.

Exploring Language
Kristen Denham has turned an ongoing blog into a website full of lessons and resources for 3-8th grade teachers interested in teaching basic linguistics.  There are lessons on grammar, vocabulary, and conventions.  Some, but not all, of the grammar lessons account for dialect differences which makes this a wonderful starting place for teaching descriptive, rather than prescriptive, grammar.

Language Variation in the Classroom: A guide for teachers
A concise website describing features of Southern English and African-American English.  There are clear examples of each of these dialects in comparison to Standardized English.  Good background information for teachers and a resource for students learning about dialect differences.

Center for Culturally Responsive Teaching and Learning
This center, run by Sharroky Hollie, provides handouts that can be used with teachers and students to explore issues of language and culture in the classroom.

University of Hawaii - Language Varieties Website
Explore language variation in world Englishes.  Gives examples of English varieties from six continents.  Includes tips for classroom teachers.

Blogs & Popular Media

The Grammar Rules of 3 Commonly Disparaged Dialects
Article by Arika Okrent describing the systematic nature of a-prefixing in Appalachian English, "liketa" in Southern English, and stressed "bin" in African American English.

The Dialect Blog
A wonderful set of blog posts about dialect and accent variation in Britain, Ireland, and America. Not updated recently, but a rich trove of past posts to mine for information.

Fostering Convention Awareness in Students: Eschewing a rules-based view of language
Blog by Paul Thomas, Furman University.  Lots of resources about critical pedagogy.  The linked post addresses descriptive and prescriptive grammar very productively.

The "ax" versus "ask" question
LA Times article by linguist John McWhorter describing the origin of the two pronunciations of "ask," and explaining why both are linguistically correct, yet socially unequal.

Dude, Guëy, Brah: Taking a stance
The Leaky Grammar blog has a variety of resources directed toward a linguistically inclined audience.  The linked post could be a fun one to use with students.

Steven Pinker: 10 'grammar rules' it's OK to break (sometimes)
Article from The Guardian advocating clarity of ideas over "superstitious" grammar 'rules.'

East L.A. speaks from its heart
2011 article in the LA Times abut Chicano English. By Hector Becerra, citing Carmen Fought.

They and the Gender-Neutral Pronoun Dilemma
From the blog Arrant Pedantry by linguist Jonathon Owen, one of a variety of posts that take up descriptive vs. prescriptive grammar and questions of modern language usage.

50-Years of Stupid Grammar Advice
Geoffrey Pullman's critique of Strunk and White's Elements of Style in The Chronicle of Higher Education.

Blogs and Resources
A post from Arnold Zwicky's Blog: A Blog Mostly About Language.  A ridiculously long list of blogs about language.  Yikes!