LastWhispered is a simple, lightweight, Ace2-based addon that stores the names of the last five people who whisper you, without repeats.
Use "/lwh list" or "/LastWhispered list" to display the list of the last people to whisper you.
This addon is still a beta version. As such, please let me know if you find any bugs!
Thanks to everyone who dealt with me asking them to whisper me constantly while I was testing this.