Leave a list of fictional characters in your journal that you would love to get a message from. Your f- and f-of-list's mission, should they choose to accept it, to write you an in-character "letter" from a character on that list. Then they post their own list in their journal and the process continues!
I'm going to list one character from a few of my fandoms, but if you want to write a letter from a different character in that fandom, you're more than welcome - any letters at all would be appreciated.
due South - Turnbull
Battlestar Galactica - Leoben
Angel - Fred
Buffy - Oz
Futurama - Zapp Brannigan
The Simpsons -
Family Guy - Stewie
Harry Potter - Aberforth Dumbledore
Hornblower - Hobbs
Any character from any Pixar film.