Genre actors in other TV shows.
For a while, the long running "Supernatural" TV show was way ahead of it's competition in the "Who can we cast as a guest star in our show who is well known to fans our genre?" competition - mostly because of it's million seasons but it has built up an impressive record. It had some nice old school actors like Linda Blair,(The Exorcist), Krychek(X-Files), Skinner (X-Files), but they really mined Joss' Whedon's alumni with appearances by Fred (Angel), Darla (Buffy) , Vi/Penny/Mag (Buffy/Dr. Horrible's Sing-a-long-blog, Dollhouse), Tara (Buffy), Kaylee (Firefly) and really reached their peak in an episode that featured both Cordelia and Spike (both from from Buffy) as a couple.
But relative new-comer "Warehouse 13" has been hot on it's heels with a lot of familiar faces - Lindsay Wagner (Bionic Woman), Tia Carrera (Relic Hunter - a late night Indiana Jones type show), Star Trek alumni like Janeway, Quark, 7 of 9, and Odo, and they too featured a fair number of Whedon alums like Amy Acker and both Kaylee and Simon (Firefly) as a couple. That's pretty hard to beat but in season 3 they at least tied their own Kaylee/Simon casting with a multi-show mini-arc that featured both Spike and GIles (Buffy)- as brothers.
