Mini aquariums are extremely popular and come in a large variety of sizes, shapes and designs. You can find everything from themed tanks that sit on a child's nightstand, to specialty minis made for plants, to minis made to enhance the room decor.
Debate gets fairly heated over the wisdom of such tiny tanks. Regardless of whether you agree that they are good or bad, there are differences that any potential mini-tank owner should be aware of. Before making a decision, do some homework. This video and article will help. Pros and Cons of Mini Aquariums (article) Pros and Cons of Mini Aquariums (video)
If you decide that you do want a mini-aquarium, these lists will help when selecting equipment. Aquariums Under 15 Gallons Mini Aquarium Heaters