www.learnzillion.com
This website is great because there are a whole bunch of lessons and videos for teachers to use. The videos are graphics that are short clips for students to have a quick glimpse as to what is going to be taught that day. They state the objective and a summary for each video. I have used this many times.
Here's a sample of what the website looks like.
www.classdojo.com
This website is great for classroom management. It uses silly looking monsters as the avatar for each student. You can set the awards and negative points for each class. Parents can use their email to link to the site and go on periodically to check on their child's progress. They can also email the teacher right on the site.
Here's a sample of the website
www.commoncoresheets.com
This website is for printing out math worksheets that are linked to the common core. Even if your district has a specific math program, it's great supplemental work or homework. You can even create test according to the standard or grade level.