This is what I use to keep myself sane and eliminate this conversation with myself:
"Did I pay that bill?"
"I'm sure I did!"
"But wait, its not showing up on my bank statement."
"What day did I do it?"
"How much was it?"
All of that is now GONE because of this lovely chart! (I know, its not really lovely...but if you like spreadsheets then it IS lovely. haha!)
In each monthly box, you can use the 'checkmark' method. But I usually write the date in there, and if there is room I will write the amount as well if its a different amount than usual.
**update** I lost my original copy of this. :-( bummer!