This website, Learnzillion, has been recommended by our state Coordinator for Math Education as being a good resource for elementary through high school teachers of math and English/language arts.
I’ve just started exploring it, but have been impressed so far with the number of lessons available at the high school level. There are 176 for math. You can choose a lesson by grade level, domain (but conceptual categories are there) and standard. The lesson includes a 3-5 minute video which includes lesson slides that can be downloaded and edited and a guided practice video. The lessons are a little dry, but would be good for a student who needs a quick review or for one who was absent. What I like about it is the alignment to common core and ideas for problems for some of the topics that I don’t currently teach in Algebra I, but will be when we go full-implentation of the new curriculum (like exponential functions).
Everything on this website is FREE and available to teachers and students.