I use a variety of things with my guys, mainly food based rolleyes
They have...
Balls to roll around to get food out
Balls with bells in (They get quite violent throwing them about!)
boxes/tubes etc stuffed with hay - with tubes, ill put something smelly like parsley in the middle, then stuff hay around it so they have to work for it and such
The metal balls on a chain that hang down, I stuff them with leafy veg, they go mad for them
Lettuce clips - can get them from aquarium type places, I just have them cable tied up, so that I can suspend veg for them, its all just about giving them different ways of giving them their food.
They also have their pigloos, cosies, tunnels etc
I think the most important thing, is mixing it up for them. Alternate things around, they're less likely to get bored