Balls
They come in all sizes, so pick one that is small enough so that your rat's feet won't fit through the air holes. You can get ones that can convert into standing wheels as well. They are made of durable plastic, and some even glow in the dark! You have to watch your rat all the time when he is in his ball. Stairs and other animals can easily hurt him. The first time he is put in here, he might be afraid, but he will soon learn to propel it and navigate all by himself!
These are the traditional wheels that are placed inside cages for the rat to enjoy at his leisure. Make sure you choose one with a smooth or small mesh running surface, because his feet can easily become caught between the bars as he is running, which is rather unpleasant. Choose one that attaches to the side of the cage rather than stands alone. This way your rat will not hurt itself if the wheel were to fall over. Also, if your wheel has a bar that goes across both sides like the one pictured to the left, make sure his tail can't get caught between that and the side support.
Rats find these to be great fun and very comfortable. Many sizes and shapes are available to fit all sorts of cages. You can also very easily make them yourself from polar fleece and a bit of sturdy wire. Just remember that anything you make into a hammock will eventually be chewed, so use safe, cheap materials. Sometimes putting a strip of duct tape around the edges of the hammock make it harder for the rats to chew it, so it will last a little longer. Make sure to remove the hammock once it becomes dirty or if the rats chew it to pieces.
One of the perks to owning a plastic add-on cage is all the endless tubes you can connect to it. There are many different varieties of tubes, from straight to a U-shape, to a spiral! You can experiment with these and make a giant maze for your pet, with a food reward at the end. They are easy to clean, but can be difficult to take apart. You can also purchase the tubes if you do not have a cage to connect them to, and just lay them out on the floor or your rat's play area for him to use. In general, small females and youngsters will fit into the hamster sized ones, but for larger females and adult males, you will need to buy the ferret size.
Many household objects can be fun toys for rats! Try tossing in a few toilet paper rolls, or a small cardboard box. Another idea is to make a piñata for your rats by wrapping a bit of food or treats in a paper towel, then hanging it from the cage ceiling in the rats’ reach. They will have lots of fun tearing at the paper towel to get the food inside. You can also string a thick rope across the cage, so the rats can climb across it, hang from it, or just chew on it. Some old children’s toys make good rat toys, like old Fisher Price houses. Just remember that whatever you put in the cage, the rats will chew, so make sure it is going to be safe for them. Also, whenever toys get dirty or smelly, wash them thoroughly or if they are not washable, discard them.
Grassy nests like the one pictured here are great beds for rats, or simply a toy they can climb on or hide in. They can also chew on them, though most rats are content to just sleep in them. Make sure you wash or replace them once they get urinated on or chewed so much they fall apart.
Hanging cage toys and play areas like the one pictured here intended for birds can make great rat toys! They tend to be fairly inexpensive, as birds can destroy toys almost as quickly as rats.
Toys made out of wood can be placed inside the cage, but be mindful of them, since rats can chew them up and make sharp edges that may be dangerous to your rats, or leave splinters that your rat can step on. Play areas like this one are best left out of the cage, and offered to your rat when he comes out of his cage to play.