Friends With Boys by Faith Erin Hicks could adapted into a great tv series: Teenager angst! Sibling Rivalry! Misfit friends! The mother left the family! The dad is a cop! Ghosts!
My favorite comic of all time ElfQuest by Wendy and Richard Pini, has stories dating back to the 1970s- there are endless plot possibilities!
My other favorite graphic novel, Locke and Key by Joe Hill and Gabriel Rodriguez, had a tv pilot shot in 2011 but wasn’t picked up by a network. There is news they are trying again! As the casting was off in the 2011 edition (Jesse McCarty as Tyler? Please), I look forward to the possibility of this going forward. (edit- Netflix now has an excellent tv adapation of it!!)
This is an obvious cheat- Outlander by Diana Gabaldon already is a tv series! IT IS PERFECT IN EVERY WAY. I love you Jamie ♥
Revival by Tim Seeley and Mike Norton is about loved ones coming back from the dead, and the fall out the ensues, would be ripe for a tv series. There have been some similar shows on television recently based on this idea, but this source material is stellar.