Think: nuclear reaction - boundless energy stemming from a tiny bit of atom... Now think: toddler - see the similarity?
Toddlers are made of energy - boundless energy that just keeps them going and going; the Energizer bunny would have a hard time keeping up!
Toys that keep toddlers entertained are toys that must be able to capture the toddler's imagination and full attention. Toddler toys also need to have good playability to keep them from getting bored. Durabiliy should also be taken into account as toddlers are quite hard with their toys.
Toy sorters are usually very good at keeping a toddler occupied. The different shapes that he needs to fit into different holes will help develop your toddler's mind while further enhancing his motor skills. One thing to keep in mind though - a frustrated toddler is not pleasant! Try and choose sorters that will allow the shapes to fit in easily.
Toys that are able to channel the use of your toddler's endless energy are also good. These toys can help keep your toddler entertained and encourage a healthy development as well.
Learning tables are a good sort of toy that provides a good mix of activity to help with your toddler's growth. Various gadgets that require pushing, pulling, turning, twisting and flipping further enhances your toddler's motor skills while developing his creativity at the same time.
Soft blocks are also quite good. Aside from the multiple printed surfaces which assists your toddler's learning skills, the blocks also double-up as a stacking toy that will provide hours of fun.
If you can afford it - and if you have space for it, playhouses are definitely the way to go.
The modern molded plastic playhouses available nowadays are built to provide a safe environment for your toddler to burn all that energy. Being the king of his own 'house' fires up your toddler's imagination. The various activities provided by the modern playhouses (tunnels, slides etc..) supplies your toddler with good physical exercise to keep him healthy and happy.
With lots of toddler specific TV programs available nowadays, the playhouse provides a good counter balance of outdoor exercise to the TV programs' mental exercise.
Good luck toy hunting!