Smallville - my favourite show of all time, I hope that Tom Welling and Michael Rosenbaum are successful in bringing their planned animated series to life.
The Frankenstein Chronicles - such an underrated and overlooked show. While it was originally meant to be a mini-series, it ended up with 2 seasons. I feel like a final season of 6 episodes is completely doable to wrap up everything completely.
Legends - needs a third season as the second ended on a cliffhanger. Season 1 was only watchable to me because of Sean Bean, but season 2 felt like a completely different show and it did not get the chance it deserved.
I would have also said Batman: The Animated Series (or a continuation of that animated universe), but there is just no way to do that without Kevin Conroy in my opinion.
1doesnotsimply