Silver dollars?
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silver dollars would look great…also any gouramis are very peaceful…angel fish look fantastic but can nip the others so id steer clear
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Boesemani Rainbowfish are colourful and, depending on the amount of fish you have and the way your tank is set up, they can be quite peaceful.

I’d also suggest Blue Rams, contrary to what some might say. They’re beautiful fish if they’re kept on the correct diet and are well looked after, and are actually very cute.

Gouramis are nice enough but they can be aggressive, particularly with mollies. Depending on the size they are at the time you buy them, they could be perfect (or not).

Labyrinth fish (such as gouramis) are more centre-piece fish, which includes Bettas (siamese fighting fish). I recommend against Bettas, though, because people are fed all kinds of mis-information about what is appropriate care for them. They are not small-tank dwellers (despite what your aquarium store owner says) and live much shorter and much more miserable lives if they are kept in the tiny glass boxes you see in pet stores. If you must have them, buy only one male and no females, or buy two females only, particularly for a tank that size. I still recommend against them, however.

Angel fish are lovely, but can also be finicky to look after – depending on the store you get them from, the genetic strain you end up with, the size of the tank and its contents (plants vs ornaments and so on). I’ve had quite a few, and although I’ve usually kept them in large communities (6 foot long tanks etc), they’re entertaining to watch.

If you really want a showfish, discus could be what you’re after. That said, they are not beginner fish, so depending on how long you have had tanks and fish, I’d suggest doing some research.

Rainbow sharks aren’t really showfish, though – they’re more like loaches, which although they are beautiful fish, if you want middle-feeders (fish that hang around the middle to top of the tank), the above might be more what you’re after.

Hope that helps!
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For general info on these fish:

Boesemani:
http://www.aquahobby.com/gallery/e_boese.php
http://animal-world.com/encyclo/fresh/Rainbowfish/BoesemansRainbowfish.php

Discus:
http://www.aqua-fish.net/show.php?h=discusfish
http://www.e-aquarium.com.au/discus_cichlid.htm

Personal experience, multiple tanks, ponds and tropical, saltwater, marine and outdoor fish (koi) for many years, as well as patience.

Discuss fish look great, i have neons as well, ive always thought siamese fighter fish looked really pretty but if you have more than one of them in a tank they kill each other. so yeah you can only have one.

Maybe more neons . .. i have neon tetras and glowlight tetras which are awesome they glow in the dark!
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Let me address a few problems first. A 40 gallon tank is too small for a common pleco.

Look at these: http://www.thejump.net/id/more-fish/Black-Adonis-Pleco.jpg
http://www.gwapa.org/articles/florida2007/images/43.jpg

If you have a common pleco, I suggest re-homing him, or taking him back to the store. You can always buy a small species like a clown pleco or a bristlenose.

Neon tetras are schooling fish, so you need to keep them in groups of at least 6. You could always go with more in a 40 gallon. Corys aren’t exactly schooling fish, but you should always keep them in at least a group of three. They need their own company, but will not actually school.

Now on to some suggestions. Rainbow sharks don’t get very big, about five or six inches at most. I’d still suggest a 55 gallon though, because they can get territorial. Territorial doesn’t mean he’s likely to kill any of your neons though, just chase them away from his territory. Don’t be fooled by the name. Rainbow sharks, bala sharks, etc. are not sharks at all. They are cyprinidae, which belong to the same family as carp and minnows.

Besides the rainbow shark, I’d suggest a gourami, maybe even a pair. Try powder blue, chocolate, pearl, or gold gouramis. They look nice in a pair, and will usually stay out in the open. A school of danios will also be pretty nice, or a school of harlequin rasboras. You could also get a group of smaller sized loaches. NO CLOWN LOACHES. They’ll get a foot long, which obviously is too big for your tank. Here are some loaches for you to look at: http://liveaquaria.com/product/aquarium-fish-supplies.cfm?c=830+885

I wouldn’t suggest rams. Despite them being very peaceful, they can be pretty hard to take care of, and unless you feel you have enough experience, I would skip on them.

Angels would also be a bad idea. If angels aren’t bullying everything in the tank around, they’re getting their fins nipped. Believe me, angels don’t look look pretty once they lose their dorsal and anal fins. I could see them killing or even eating the guppies, and I can see the mollies nipping the angels.
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angels and gouramis.
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