Dither Fish (recommended by a friend), Zebra Danios, platies, guppies and a few bristlenose plecos and synodontis catfish. The Fire Eel loves this-puts him at ease, hand feeds, very tame. 90 gallon tank with ultra smooth S-grade 3M Colorquartz-bigger home required later....
A Paroon....I can't see that working out long term IMO but hey, you never know! I have a Paroon and they will need 1000 gallons plus at some point.
Enjoy your Fire Eel. They are awesome.