Hi Jennifer
Hmmm.....well I think the most successful toys are:
1. A wheel. Must have! Must be solid (not runged or mesh) and BIG ENOUGH FOR THE HAMSTER!!! Many "hamster" wheels are really only big enough for dwarves.
2. Cardboard to chew. Some hamsters don't go for this but my Phoebe loves it. She always has a loo roll on the go, and sometimes I'll make up little packages with carboard, with treats inside, wrapped up in tissue.
3. Tubes/tunnels to run in - whether as part of the cage or as a separate thing inside the cage. Hamsters seem to love being busy running about their little empire.
4. A sand bath (just some chinchilla sand in a jar on it's side) - again some hamsters don't go for it, my old Campbells Alfie loved his. Keeps their coats in tip-top condition too.
5. A loving human!!! The best playtime is out of the cage, free range exploring a ham-proofed room or hamster play pen, sofa-mountaineering (under close supervision!!) or just being handled
Exercise balls (clear ones) are ok but don't use them for too long.
What not to buy......anything too small. Make sure tunnels/holes are big enough for your hamster to fit through comfortably. Make sure the wheel is big enough that the hamster doesn't have to arch their back to run in it, and that they're not rubbing on the spoke in the middle. Also be aware of cleaning practicality - wooden toys can be great but they might get chewed and can't be sterilised for use with your next hamster, just things to be aware of.