Simon R. Green does this sometimes when he throws his characters from one series into another.
Terry Pratchett just jumped even further into my favorite author spot last week by bringing back a character.
I've always loved Pratchett's Discworld. It's been my favorite series and setting for a very long time. My very first, and only if I remember right, cos-play character was Eskarina Smith, the female wizard, from Equal Rites. It was a my first Discworld book and holds a special place in my heart. This was the only book she was ever featured in.
How awesome is that? After 35 other books, Pratchett brought back what happens to be one of my favorite characters?
My absolutely favorite author ever.