This is a rather difficult question to answer, due to the fact that there were so many other characters added when it became "unlimited", and because of the fact that with so many different ones, only a very small handful ever got used often enough in stories to judge. Still, I'll try my best: Green Arrow, Wildcat, Huntress, Supergirl, Dr. Fate, and Zatanna (though I wish they'd used her more updated costume, not the old one). I was also disappointed that the Red Tornado never got used very much, and was it my imagination or did the character lisp? That's kind of weird, if he did, considering he was supposedly an android.
(an aside, if I may... How is it that Green Arrow's ex-sidekick was made a member of the JLA and Batgirl never was? I know, Barbara was never officially Batman's sidekick, but I think she deserved it far more than "speedy"... or whatever name he goes by now)