Hi
I have a 55 gallon tank as well, Ive had some stocking problems with my time with the tank. My tips would be
1. Plan your stocking plan in advance and research each fish and ask questions on boards like this.
2. Try not buy on impulse ever it will throw your stocking plans way out, if you fall in love with a fish and feel the impulse ask the shop to reserve it then come home and research it first. (this has happened with me and ive had to take fish back because of problems)
3. Try and stick to 1 focal fish species per level, one for top, one for mid water and one for bottom. Then have smaller fish and schools around them.
Some fish sugestions, I will allways promote keyhole cichlids I know you said no cichlids but, these are very peaceful and mine never fight with each other or any one else at all and very hardy they survived a week in bad water when my filter failed and recycled. When they are adult they are white with black markings and the male has blue tops to his fins, they get to around 4 inches and do best in a pair.
Or you could try gouramis? If you have a well cycled filter you could try some of the more delacate species like chocolate or licorice. Or you have the more common types like the blue gold or pearl. Pearl gourami are often very peaceful, where as the blues and golds are quite agressive to each other so with the pearls you could get two a male and female (the males have a red chest females have white chest) or one gold or one blue (three spot gourami are the same)
If you want a big schooling fish, how about silver dollars? If your tank is planted ignore this as it wont be planted for long with these lol they are herbivores and eat as much plant as they can. Or you could do dension barbs, sometimes called rose line sharks but they are barbs and need to be in schools big silver bodies with yellow tails and a red stripe down both sides of the fish really bright as well. Both of these 2 fish get to a big size and would fill the tank quite well for them to feel safe you would need about 4 in the school.
You seem to really like the cory catfish idea

I like cories there are some gorgus species out there and you would be amazed at how many there are (they have stoped naming them now and started a number system called C numbers now) You could say get 10 of these, they would love it! But if you do get 10 get all the same species, different species will interact but if you have one species they will school all over together and play and race etc, I really like sterbai, pandas and skunks. Peppereds are quite nice as well. For a feature fish on the bottom you could look at some L number plecs, like the gold nuget (green with gold spots) or a bristlenose or rubberlip or peckolita species (lots of pretty ones). Or you could look at some of the smaller Syno catfish, multipunctatious (sp) stays around 5 inches or Euruptious (sp) gets to 6.5 inches there are more but im not to good on names lol.
An alternative to cories as well could be dwarf chain loaches? I really like them but they can have a high price tag around £10 each ($20) where i live.
Also for schooling fish you said about neons, I would recomend cardinals as neons are sometimes weak due to inbreeding to meet demand in the stores, cardinals grow a bit bigger and are often more colourful than neons aswell.
For an interesting school you could have hatchet fish, they are surface dwellers and come in different types, like marbled, black and silver etc. You need a cover though as they can jump!
There are so many schooling fish out there one of the best things to do would be to go to an LFS or 2.....or 3 and see what you can find.
A stocking from me would be
Pair of keyholes (male and female)
5 Marbled hatchet fish
8 Cardinal tetras
8 Corydora sterbai
1 Gold nuget plec
Using the inch per gallon rule these fish take up 50 gallons (if ive got sizes right, did it from memory), which is probs the amount of water in there due to decorations and gravel.
Sorry for writting so much ^^'''' I got on a bit of a roll

hope I've helped a little ^^
www.aquahobby.com <------ I find this site really helpful its lots of people writing reviews of their experiences with the fish species they have loads of different fish listed in the gallery.