I find that my rabbits are much more interested in "new" things, even if they're just the old things moved around. They're smart animals, so they get bored with the their stuff. Take away some of his toys and give him some different stuff. In a few weeks, switch them again. Voila! New toys! Move his tunnels and boxes around so he has to relearn how to run around and through them again. This always gets my buns busy.
Treat dispenser balls are fun- I just got a few. Put a few of his pellets or a little bit of dry treats like oats in it, and watch him have fun working for his food. I also like to stuff hay (especially special stuff like oat hay), chew toys, and a few treats into a paper lunch bag, tie it shut, poke holes in it, and give it to the buns. They take hours shredding them, munching on the yummy stuff, and throwing them around.
Try building mazes or castles with boxes, and hide little caches of hay and shredded newspaper in them.
Along with rabbit hopping like Mikoli does, you can do simple things like teach him to run after you for a treat when you call. Snuggy's Mom did this when she had to help her bun loose weight. Snuggy would run all over following her mom, and then get a small treat at the end of it for her hard work.
And check out Bunny 101 for more cheap, fun toy ideas.
