Just a reminder, these are sculling drills. In most cases, you could probably create just as good sweep drills from these as well, however. Square blades, feet untied, or both at the same time is a favorite of mine. It can also be applied to almost any other drill to make it a little more challenging. Balance is so key in our sport that learning to row square blades early on was a big plus for me.
Pause drills with blades off striving for set at any position on the recovery is pretty standard.
There are lots of variations of this. Pick drills are also pretty standard. I think they're often overused though. In the right situation, they sometimes do some pretty amazing things. Doing them square blades is a good balance drill.