Teachers Pay Teachers- This website has everything! You can buy or sell lesson plans and unit plans. It has been particularly useful for me if I want to print out a quick worksheet for sub plans or if I want some supplemental activities to go along with a lesson. Most of what I end up downloading is free, however, I will spend a couple dollars or somthing if it seems like it will be useful to my students.
Brain Pop and Brain Pop Jr.-These two websites are phenomenal for visual and auditory learners. There is short video on just about every topic you can imagine. I found it particularly useful for math concepts. It does require a subscription, however, I think it is well worth it.
Go Noodle-This is a website that helps to facilitate "brain breaks" in the classroom. These physical activity breaks get students more engaged and focused so that they can truly retain the information that is being taught.