I have had a
redtailed shark (E. bicolor) for a couple of months now, and absolutely love it! It is a beautiful fish, and only grows to about 6 inches, so it won't outgrow a 55
gal like balas would. It has to be kept as the only one of its species in a tank, and really shouldn't be kept with certain conspecies (did I get this word right?) like the flying fox. As redtails grow they tend to become more aggressive, so that would be something to keep in mind.
According to Elmer the peacock eel would get along fine with the redtail. I have read that dragon fish need salt in their water, which would not be very good for the redtail. I don't have any experience with either the eel or the dragon fish myself, so you might want to do more research on their compatability. The giant danios should be okay. (I currently have my redtail with some Buenos Aires tetras, and they get along just fine.)
My redtail is an absolute hoot to watch. He is always slinking over the rocks and plants, as if he were cleaning them off. (He does not eat algae, though.) He will shimmy up a leaf, flip over to the underside of the leaf, and go down it upsidedown.
If you decide it is compatable with the other fish in the tank I would highly recommend it.