I really enjoyed the android Hourman. He had a great solo series that was pure fun and heart. I believe he was last seen giving up his life to save the original Hour Man in some sort of time distortion. He’s been gone for thirteen years.
I miss Linda Danvers, but as long as Kara Zor-El is around (and starring on a CW show, not to mention possibly getting her own film) it seems unlikely she’ll reappear. Another favourite of mine is Connor Hawke (who is at least showing up on Arrow, although as a totally different character than he was in the comics), but I don’t see him being reintroduced thanks to Ollie’s de-aging with the New 52/Rebirth.
I want to see the “replacement” Aquaman from the (excellent) Sword of Atlantis. I think that story line was roughly 12 years ago.
Also want to see the Charlatan return. Go read “Dead Reckoning” from Brubaker’s run on Detective Comics. It lasted 5 issues published roughly 16 years ago, and was sadly overshadowed by Hush (still ongoing at the time). Still one of the best Two-Face stories ever. One of the best Joker stories too.