Here is a wide selection of treat toys to keep your dog amused and use its brain to solve the problem of how to get the treats out of the toys.
I strongly recommend that a wide variety of treats and dog food are put into the toys so that the dog is tempted by the wonderful scents and keeps working the toy in order to get the most tasty treat out. Also try to encourage your dog to play with the toys on your lawn so that when the treats fall out the toy they are hidden in the grass. Then the dog has to work even harder with his nose to check whether he has missed a treat while playing with the toy.
Some of the toys are simple and are ideal to introduce your dog to the concept of "working to get a treat". Eg Molecuball and Twist N Treat.
Others toys are soft to the touch (eg Monster Mouths) and are popular with dogs who do not like hard plastic in their mouths. However, these may not be suitable for dogs who have a history of chewing and destroying toys, in which case treat toys such as the Squirrel Dudes may be the solution.