Repl.it---Repl.it is a simple and powerful online compiler that allows students and teachers to work in over 50 different languages. Teachers can set up classrooms and create assignments for their students or you can find an already created classroom that you like and borrow from it. You can even set up auto-grading, which will save you time in the long run!
CodingBat--CodingBat has a series of code practice exercises that you can assign to your students for either Python or Java. These are a series of small problems that are designed to help build skills and syntax proficiency.
Khan Academy--You can create a Khan Academy classroom just for computer science or programming. The courses offered range from computer programming to computer animation, and all of it is graded for you by Khan Academy.
Runestone Academy--This is a website that contains a number of open source, free books and activities. Like the other sites listed here, Runestone will allow you to make a classroom and give students assignments. Included on the site is an AP CSA review that I use every year and that my students have found to be very helpful. The site also contains books on Python and data science, along with exercises and projects that you can use in your classroom.
GitHub Classroom--This is one that a lot of us tried a few years ago and found to be a bit unwieldy and difficult to manage. However, it may be time for you to revisit GitHub classroom. They have a new classroom assistant that makes grading so much easier and that can be integrated to work with an LMS and third-party testing.
NICERC--If you are teaching any of the courses in the new cyber security pathway, I am sure you have heard of NICERC. But, if you have not, they have a bunch of great resources for you to use. They offer curricula for a number of STEM/STEAM disciplines and much of it is hands on and project-based.
WETeach_CS--his year, WeTeach_CS from the University of Texas at Austin has rolled out their new computer science A curriculum. It is free for this year, so sign up and give it a try.