Atar Notes has some revision lectures that can be helpful to go through each topic and remind yourself of what is involved and try some practice questions. Good for exposing big areas of weakness.
mcgrathematics has a playlist of ext. 1 topic vids on yt. havent used them much personally but they seem pretty good. (wont let me link for some reason)
Prof Dave explains has some good videos, though not specific to the hsc so you may have to dig around a little bit to find what you need (and make sure you aren't doing stuff outside the course)
Also khan academy has heaps of stuff.
