Cory cats would be one that would be likely to breed in the environment you describe. As for other small fish, the list that Lupin so generously provided contained a number of species I would never suggest mixing with guppies, and because they are egg laying and/or egg scattering fishes, are unlikely to spawn successfully in a community tank.
I can think of 1 specific fish that would meet all of your requirements... coral platy. These are a dwarf species of livebearing platy, and the ratio for them is the same as the guppys (at least 2 females to each male). Coral platys tend to be a very deep and vivid red/orange in color, and are peaceful with the same breeding habits as the guppys.
There is quite a long list of compatible fish for what you wish to create, but as I said, the likliehood for most of them to breed is just not there. If content with not having babies from every type of fish in the tank, some quick ideas for you to consider that are peaceful enough to put with guppys, and quite common on the market, bright in color, schooling, and somewhat "easy" to keep...
Neon tetras (I would suggest neon instead of cardinals, they tend to be sturdier and the pH requirements differ with the cardinals and guppys)
glo lite tetras
lampeye rasbora (these are pretty in a school with their blue eyes glowing in the reflection of the lights and stay fairly small like the rest)
green fire tetra (the green is almost irridescent, the red/orange is vivid once they're settled in and mature, and the white is so bright it just sets this fish on fire! These are one of my favorites of the smaller tetras, and they're peaceful)
pygmy cory catfish instead of any of the standard cory catfish
or panda corys (the pandas stay smaller than most of the others and the pygmys stay very small)
the list goes on, but these are the ones off the top of my head that I would suggest you google, take a look at what they all are before making your choices. Even in a 90 or 110 gallon tank, a few spawns from guppys and/or other groups of fish in the tank will send the population soaring quickly. Be prepared to not see many fry survive, even in a heavily planted tank, if there are a large number of other fish in there. The other fish will eat the fry if they find them or can catch them, and some fish know to hang out in the right places around a female giving birth in a community tank.
If you have questions about any of the fish on any of our lists here, let us know, we're happy to help.. and be prepared to take pics, I want to see this tank when it's finished, it sounds beautifully planned.