Google Ngram Viewer is a great tool, especially for rough-and-ready searching and visualization of linguistic trends, and as a teaching tool to introduce students to lots of interesting questions we can ask about language variation and patterning. I use it all the time.

Digital citizenship is one of the big things we talk about on Edudemic. It's basically being a good person online. Being a good person involves a lot more than just not spamming or trolling, mind you. It involves keeping yourself and your friends safe.