Hey guys... I'm thinking of getting a few more fish next weekend, and I really want to add some more fish that are vibrant and attractive, and who will happily fit into the community I've set up so far... which include:
5 X-ray Tetras - 1 inch each
4 Glass Catfish - 2 inches each
4 Guppies (same sex) 1 inch each
2 Mollies - 2.5 inches each
5 Gouramis - 2.5 incheas each
1 Red clawed crab - 1 inch
1 Shrimp - i inch
1 Khuli Loach 1.5 inch
1 Red finned shark. 5 inches

I should also note that the tank is 260ltrs. Also, how many more fish would you sayh I'd be alright to put in?

you could try those new glofish. they're available at any petco or petsmart. personally, i prefer petsmart. GloFish - Tropical - Fish - PetSmart they look pretty colorful to me.

The glofish are 'new' fish - the result of gene transfer experiments in labs. I would never buy them myself - what can you learn about nature with a test-tube fish? If you're studying DNA, that's one thing, but in the tank, they're frankenfish.
There are hobbyists breeding and selling them locally, but they are illegal to sell where I live. I think that may be the case in a lot of jurisdictions.

The fact you posted in liters means I don't know what's available where you are. It's always better to check out the possibilities and ask about individual species - I could suggest things that aren't around where you are, etc. Here in Canada we have different fish available than in the US, and that holds true across the board.

Von Rios Tetras are very bright, in the orange range. Harlequin Rasboras are shiny like a copper penny. Honey Sunset Gouramis are very colorful, and good community fish. I wouldn't buy the glofish, because they look unnatural to me. But there is a Glolight Tetra that is very nice. There are many types of Cories you could consider to add some black and white to your tank.

I'm not a big fan of the glofish either, just something very...mutant like about them. I second the vote for gourami, as they are very beautiful fish.

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"Being ignorant is not so much a Shame, as being unwilling to learn".-- Benjamin Franklin

Hey guys, thanks for your suggestions. I've got some gouramis, and I agree, they are beautiful fish. Also have two mollies, both black and white lol. I have seen the Glofish and not such a big fan of them... Too unnatural for me.

Other than glo-fish, what is the most colorful, beautiful fish that is also peaceful for a 20 gallon?

Glo-fish are illegal outside of research labs where I live.
The best way to go is to a library. Look up a general fish book, and read through the tetras. With text and pictures, you can make an informed choice. There are literally dozens of possibilities.
Tetras, small Rasboras, small barbs, ricefish, lampeyes, livebearers - the choices are huge, and without pictures, how will you know what you like?

Okay, ill get one, but if I have to get an amazing fish as a present by tomorrow, any ideas?

Amazing fish, with no worry about what else is in the tank, in a 20, as a present? That's a fun thought.
Iriatherina werneri, the threadfin rainbow;
Apistogramma borellii;
black neon tetras;
rummy nose tetras;
Fundulopanchax gardneri killies;
platys;
pygmy corys;
wild type bettas;
norman's lampeye;
glowlight tetras;
cardinals;
neons;
flagfish;
croaking gouramis;
Tateurndina ocellicauda;

and after that, I'd have to think about it. An empty 20 gallon is fun for an aquarist. Most of those fish would only be found in a good shop, but all have been seen where I live in recent weeks.
If you are buying as a gift though - it has to be compatable with what's already there. Fish surprises can really create problems if a friend's tank is crowded, has predators, etc.

Maybe a nice,, fancy goldfish? They're very pretty.

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16g-1 unknown wild minnow, 1 bolivian ram, 2 neon tetras,2 khulis, snail
55g-1 red tail shark, 2 banjo cats,
2 silver dollars

Are all of these somewhat peaceful?

At my LFS they have endlers livebearers that are just gorgeous.

Celestial pearl danios are also lovely, they look like little trout

id go for danios, there really fun to watch and pretty, also rummy nose tetra and......another one thats really really pretty, when i remember the name ill post it. if your in the UK you can get these fish for very cheep especialy in places like pets at home.

denison barbs