I’ve just set up a 55 gal cold freshwater aquarium and I’d like to fill it with some very colorful fish that won’t fight. I’d like to have as many different varieties as possible, with a wide range of colors and patterns. I’ve stocked the tank with plenty of hiding places, with caves, plants, and fake coral. What types of fish should I look into?
Thanks 
Neon tetra
Mollies
Swordtail Platty
Rainbow fish
Rasbora
Clown Loach
and of course the boring little goldfish
I particularly like neon tetras
[my brother kept a freshwater aquarium for years. I cant keep an airfern alive, so I know my limits ]
Thanks! Those certainly are colorful, and I’ve already promised the SO that we’d look at Clown Loaches, so he’ll be glad you mentioned it. I notice all of these are smaller fish, will nothing a little bigger play nice?
There are several different tetras that are attractive, not always available at average aquarium stores. Although they’re a bit more aggressive than those listed, I’d add in the gouramis (blue and pearl, which is an opalescent pink) – they’re not fighters but can have very dominant personalities in smaller tanks, so are best in larger ones. But very pretty and easy-care.
When we kept fish, some of my favorites were:
Schools:
Neon tetras–very small, bright little fish. Usually quite cheap and easy.
Cardinal tetras–similar to neons, but with red instead of orange. More expensive and more fiddly.
Rummy-nose tetras–one of the prettiest of the little fish, to me
Tiger barbs–attractive colors, but shouldn’t be put in with anything with flowing fins. No bettas or guppies, for example.
Corydoras julii–I don’t think they need schools, but are neat in schools
Glass catfish–so gorgeous in schools. These can’t handle much current
Pairs:
Pelvicachromis pulcher, or Kribensis–pretty and neat to watch since they herd their young. Tend toward the bottom and like caves.
One mail, two or three females:
Platies and swordtails–they like hard water
Probably not a good fit for the others unless you want to specialize:
Goldfish–should be in a cold water tank with a lot of room
Mollies–should be in a brackish water tank
Fish are pretty opportunistic, in general. If they can eat another fish, assume they will eat another fish.
The gouramis Polycarp mentions can get fairly big and very spectacular. There are also dwarf gouramis that are smaller and very colorful.
I’m a little nervous about getting one of those, my mother had one and it attacked one of her other fish, they were in a 10 gal tank, and it was really aggressive.
If I remember correctly, and I might not, gouramis should always be mf or mff, and I think they like hiding places and can be aggressive with one another. But there are so many types of fishes, I’d say just avoid any you have any fears about.
A couple other species:
Serpae tetras
If you wanted, you could do a whole tank of rainbow fish. Boeseman’s Rainbowfish is my favorite in coloration, but I’ve never kept them. They do get much bigger than the tetras and the like.
http://www.fishchannel.com/fish-exclusives/fama/colorful-freshwater-fish.aspx My first thought was African Cichlids. They are much more interesting than most fresh water fish.
Barbs ,if memory serves me right, are fin biters. They will make some pretty fish ragged looking.
Angel fish and Discus are the top of the fresh water fish for looks. They are not aggressive. Discus have a specific PH range that requires peat to maintain.
Tiger barbs can definitely be nippy.
African cichlids tend to be aggressive. Very pretty, but not as easy in a community.
Oh geez, where to begin?
First of all, most of the fish named above can not go in a cold aquarium. If you want a variety of colorful fish, You really need to invest in a heater. It’s really not that expensive, I recommend the “Stealth” I think about $30 would get one to heat your aquarium nicely.
Second, do not consider Clown Loaches for a 55. I have some in my 100 gallon, and I feel constantly guilty that I can’t afford to provide them with more room right now. They can get up to 12" if properly cared for.
So the rest of my recommendations will assume you get the heater - without it you’re pretty much limited to goldfish, (3 goldfish at most in a 55!) or a few silver-grey varieties. Oh, and never mix goldfish with other types. Goldfish put off a huge amount of ammonia, and they have a really goopy slime coat which chokes other species gills.
OK, so you know you want color and variety. You need to think in terms of school size and strata. You’ve got a 55 gallon, so a good general rule of thumb is 1" of fish per 2 gallons of water. Remember that measurement begins with the adult size of the fish. Done properly, your tank will look a bit bare at first.
Pick a bottom feeder, a middle, and a top feeder. (Since you like CLs, maybe take a look at Botia Striata. Zebra Loach (Botia striata) — Loaches Online same color scheme and personality, smaller adult size.) Otherwise I’d stick with cyprinids. Harlequin rasbora go really well with loaches, but you’d need at least 10 for them to be comfortable, and 15 is better.
On the other hand, if you’re looking for a ton of movement and variety, you can’t go wrong with buying good guppies. I don’t mean the barely raised ones at the pet store, but cruise Aquabid and liveaquaria for the really good ones.
Also think about lifespan. Loaches live a long time - it’s a huge commitment. Guppies and rainbows, a year or so; so if you change your mind, you don’t have to wait as long.
Consider shrimp. Don’t mix them with loaches or bottom feeders, but you can’t beat cherry shrimp for color and interest.
Also keep in mind that you can add color with decorations and plants.
Check out the fish compatibility charts here: http://www.badmanstropicalfish.com/fish_chart.html and go chat at the forum there. Those folks are extremely helpful and mostly quite knowledgeable. Tell them TruCelt sent you and they’ll give you the secret handshake. 
Lastly, for a 55 you need a python. Like this: http://www.fosterandsmithaquatics.com/product/prod_display.cfm?pcatid=3910&ref=4032&subref=AA&mkwid=S23tiFX5i|pcrid|4166653206&cmpid=PPC--G--4032 You’ll never maintain a proper routine (30-50% water chnage weekly. Yes, really.) schlepping water in buckets.
I saw the freshwater part, but not the cold part. Mea culpa.
Ok, so we’re going to buy a heater tomorrow for sure, and I’m thinking atleast a Clown Loach or two (the SO won’t budge on it). Are they sociable?
African cichlids tend to be aggressive. Very pretty, but not as easy in a community.
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I love these, especially the bright yellow our Petco has! I’m just worried that they will stress out anything else they are with.
If my tank was a 55 I’d go with five or six types of smaller African cichlids but they can’t be mixed with other fish. They are aggressive and need harder water. So, I’d go with a more traditional community tank in your case. My personal opinion:
Two or three yellow gouramis.
Two or three blue gouramis.
Two dwarf gouramis (very pretty red and blue stripes).
Six or seven tiger barbs (they are horrible fin nippers but in a group that big they mostly nip each other).
Three clown loaches–if you have someone who’ll take them if they get too big.
One small or medium species of Pleco (not common!)
Four red platties.
You have captured the heart of my SO, he wants to take your list to Petco and get them all! 
Will all of these live peacefully together? Will they have enough room?
as for your concerns dwarf gouramis are not usually aggressive. They’ll not be too troublesome in a 55 gallon. Anything slow enough to get caught by them will be too big to be bothered.
they should all be fine. I kept just abou half those numbers in a 30 for years (minus the loaches)
don’t add them all at once though. Take your water for testing untill ph ammonia and nitrates are at proper levels, then start slowly. I’d add four tiger barbs first, then a week later test the water and add two more And the platies. Once that water is good, you can add more fish. Save the loaches and dwarf gourami for last as they can be sickly.
A slightly larger, more aggressive fish you can add is the red tailed black shark. He, the loaches, an the pleco don’t eat normal food though. You’ll need algea chips.
Oh and if you ever want to ask questions drop me a pm an I’ll be happy to help.