Many rabbits ignore toys. They do like to explore things, so cardboard boxes, cardboard tunnels, paper grocery bags... things like that are a fun option. They chew them too and can get bored of them. So going with something free (like cardboard boxes) is a good option. You can re-arrange them and trade them out for other size ones when the rabbit tires of a certain arrangement.
Here's an informational site (does not sell anything).