(Based on a list by @teachersarahzgz)
Remembering
I can clearly remember…
I can vividly remember ...
I distinctly remember ...
I think I recall something about...
As far as I can remember...
As I recall, ...
If I remember correctly, ...
If I'm not mistaken, …
Unless I'm mistaken, ...
I have a vague recollection of...
That rings a bell...
If I cast my mind back to last week’s class, I think I remember...
Forgetting
I have (absolutely) no recollection of that (whatsoever).
I don’t recall that (at all).
I forgot all about it.
I fail to remember…
It escaped my memory.
I’m afraid I’ve got a short memory. I can't remember.
It’s on the tip of my tongue but I can't remember.
Nope...My mind is blank /My mind has gone blank.
Asking to be reminded
Can you refresh my memory?
Can you jog my memory?
Could you please remind me of that?
I have completely forgotten, so please enlighten me!