Help with type of fish in 30 gallon aquarium..?

Try African cichlids ;)

The eel is already going to take up most of your potential tank space. I wouldn't add more bottom dwellers or you are going to have a very bottom-heavy setup. The cories probably wouldn't be a good match because they are very active fish, always buzzing around the bottom for food, while the eel is much more passive and would probably be stressed by all of their activity. In a bigger tank, say a 55 gallon, I wouldn't object to housing the two together, but in your tank, there's just not enough floorspace for them both to live hapilly. I wouldn't get a pleco either, as they are extremely high waste producing fish. A common pleco is off limits entirely. If you must get one, get a single bristlenose or rubberlip pleco. Just keep in mind that I'd you put that with the eel, the bioload is going to be pretty high, and you couldn't get as many other fish as you would probably like. Here's what I suggest: First, get the eel a ton of things to hide in and under. For cleaning duty, opt for 3 or so nerite snails INSTEAD OF the pleco. These snails will eat algae, unlike the mystery or apple snails. They will be much lighter on the bioload than a pleco (even a small variety) would be. Fill out the top with a school of 6-7 dwarf or marble hatchetfish. Finally, fill out the mid levels with a school of small barbs or medium tetras. Some cherry or rosy barbs would bring some nice color to the tank. For a great look, include live driftwood and a densely planted back area, with some open area in the front for more active swimmers. A note on the peacock eel: they require a special diet and can be picky eaters sometimes. They also prefer a finer gravel or even sand ax they like to burrow, but if you provide a multitude of caves and such you don't have to worry excessively about getting sand.