Good General Sites when you need to look for something!
Great explanations with exercises.
Yes, it is a German-based site, but with great resources--explanations and exercises
Very abbreviated lessons; most with exercises.
Lots of exercises on a variety of topics
Learn English Feel Good
This website may not have explanations, but such a wealth of exercises--great for when your students need extra practice--great upper level resource!
Not very colorful, but each page has a short explanation with several quizzes at ascending levels.
Not the flashiest site, nor the most complete explanations, but the exercises are very good.
Guide to Grammar
Road to Grammar
You have to scroll through an alphabet list, but you'll have a lesson and quiz.
Voice of America Everyday Grammar TV
Yes, Voice of America has grammar video lessons, and they're quite good! No exercises, though.
Lots of varied worksheets to introduce and practice
Too and Very
Few and Little
Explanation and exercises