|Art by yours truly, Rafa Rivas.|
The first clear example would have to be J'onn J'onzz, the Martian Manhunter. When the Justice League of America was founded, outside the "super trinity" (Batman, Superman and Wonder), he was about as famous as any of the rest. Really. In fact, the weakest link was Green Lantern, who debuted some months before the team was created. After the debut of the JLA, all its members were editorially pushed with their own titles; the Martian moved from Detective Comics, where he was out-shined by Batman, to House of Mystery, where he became the lead. The Elongated Man replaced him in Detective Comics. However, that all faded by the late 60s; he was first taken out of House of Mystery, and then, he was written off the Justice League. By the 70s, he was known as the green bald dude who was somehow a funding member of the JLA. After over a decade of cameos, the Justice League title provided the best justification for his return: it needed full-time members, who wouldn't have adventures outside the book. Lacking options to make the team feel like the real JLA, writer Gerry Conway decided to bring the green dude back, and for similar reasons, the next creative team kept him as leader of the Justice League International. DC revamped the League once more in the mid 90s and, this time, the angle was going for the original founding members (or their available equivalents). Consequently, after all that, despite his long absence around the 70s, the Martian became known as "the heart and soul of the JLA". That's a happy ending, let's see how it continues now that he has been retroactively erased from the origins of the Justice League and shoehorned into a team called "Stormwatch".
Firestorm popped up in '78 with a mini series, then, fully boosted by his creator (Gerry Conway), returned in 1980 to join the Justice League and get his backup feature in Flash. In 1982, he graduated from the backup to get his own title. Then, they got the popular characters out of the JLA title, they did some really weird stuff with him in his book, yadda, yadda, yadda, he didn't appear through the 90s. When I started reading comics, I often wondered whatever happened to the guy from Super Friends with fire instead of hair. He returned, but they keep doing odd things with the character.
Their absence is normally a bit more notorious once they return; however, I believe I can identify the missing people of this era. My criteria is how recurring they were in the past, compared to what they get now:
10. Zauriel and Aztek
Shooting stars like Ragman or Blue Devil, they were never really regulars of anything. However, their absense is odd, considering that their creator, one Grant Morrison, is one of the most influential forces of the current DC Comics authors. He tends to leave a trace of brilliantly conceived bastard children behind him.
9. The classic Teen Titans
8. Black Lightning
7. The Penguin
6. The Question
4. Green Lantern John Stewart.
2. Wally West
1. Elongated Man & Wife