Discus

Angelfish
Cardinal tetras, harlequin rasboras, rummynoses or tiger barbs...
You could do like 20 tiger barbs, an RTBS and a bristlenose plec - I did that a while back in a planted tank - it was incredibly entertaining.
Or 40 cardinals or rummynoses

Or 40 harlequins. Or 40 tetras/rasboras/barbs of your choice (depending on their size of course

Pearl gouramies (I've done that one too) - wonderful but you'll want a plec or two to fill out the bottom layers. Or cory cats.
Croakers or sparklers. They look great in a planted tank.
Or you can beat me to the badis badis species tank I have planned.
Then there's all sorts of cichlids - pulcher/kribs, rams (german blue/gold or bolivian), keyholes, apistos, all sorts of dwarf cichlids. Anything realy that won't tare up your plants

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You could also get a trio of fancy guppies and see how quickly they fill up the tank - that's something I am DETERMINED to someday do... Or substitute guppies for platies, mollies or swordtails.
Something else I want to do - get 25 zebra danios. When was the last time someone got some of these because they are such beautiful and active fish with great characters? I mean everyone seems to use them for cycling or maturing tanks so I think they deserve this more than many other species do.
Another species I've considered (well not realy a species tank) would be lots of algae eaters like flying foxes, siamese, false siamese and otos. They all look pretty similar, have similar requirements and would enjoy a heavily planted 55 gallon...
Or maybe get a single chinese algae eater (yes I'm gonna do this one too

) and see how big you can get it to grow...

Oh, something else I've tried (and had great success with), is a female betta community. If you want color (and activity) - that's deffinately the way to go. You could get 25 bettas (females obviously) in there - imagine that...
You could also go for different cories and get pygmy/dwarf cories to fill out the middle layers. The rest would be pretty much bottom-dwelling though. But think how many you could put in there... You could have a shoal of 10 bronze, 10 blackfin and 15 dwarf/pygmy - those are just my favourites - you could obviously choose the species

The possibilities are Endless... Oh, what about Endler's?

Then there's more unusual fish... Things like headstanders or anostomus would be fun.
Pencil fish
Rainbowfish would be incredible...

Don't know what else to suggest.
