I kind of like this question. Its looking for obscure or infrequently used characters.
There are dozens of powerful villains, but I'm guessing you're looking at heroes. In addition to those you mentioned, there are some others, most of which are women.
Nightshade is one: her access to another dimension for teleportation powers and her control of shadow demons make her very formidable.
Firehawk is another. She has fire powers which are up there with Firestorm's.
Harbinger is a first-rate powerhouse, capable of replicating herself and deploying powerful energy beams.
Lady Quark has nuclear energy powers.
Captain Comet, the sole male in my list, has powerful mutant telekinesis.
And Looker, a vampire telepath, must certainly be almost unbeatable.
