A cool and rare badge would be to get a badge for reaching the daily cap limit solely on a single answer and another badge for reaching your daily cap limit on a single question.
You can still gain rep from other answers but if your cap limit is already reached a hidden running rep count will continue. Should that hidden rep count for that specific answer / question be reached, you get the badge.
This would also take into account the +15 if your answer is accepted or +2 if you choose an answer for a question you asked.
I am not sure of what the badge would be named. Maybe some ideas?