Personally I find cats to be the least amount of work, followed by fish. If those are out you are looking at something that needs it's cage cleaned frequently.
Rodents actually require a lot of work and smell very bad if it's put off. Out of all of the rodents I kept, mice were my favorite. They were easier to take care of and they were not great at escaping. I recommend keeping any rodents in a glass aquarium (the "long" ones, not the regular "high" shape) with a metal mesh lid that clicks on well. Hamsters especially will get out of any plastic cages designed for them.
Depending on the work you are willing to put in and the amount of interaction you will want with the pet, rabbits and ferrets are good pets that can be litter trained and that can be out and about in the house, but only supervised unless you want some very unpleasant surprises.
One of the easier non-mammalian critters I ever had was aquatic frogs of some sort. They required about the same amount of maintenance as fish. I kept them in an aquarium with a low level of water and some aquatic plants and rocks and stuff. I honestly don't even know what they were.
Some lizards can be easy enough, but getting started can be expensive. Anoles are cute and probably the easiest reptiles to keep and they don't need a lot of expensive equipment.
And yes, my house was practically a zoo
