All three of my gliders love the wheel, not doubt about that! <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />
Other favorites that sort of vary between the three are barrell of monkeys (my little girl gets in the barrell and rolls around <img src="/ubbthreads/images/graemlins/roflmao.gif" alt="" />), feathers (two of mine like the big feathers and the other one likes smaller feathers), fake plants or leaves, and little cats toys (like the balls either with bells or the crinkly ones, jacks, and mice).
My boys love their foraging unit from Sugarae's Attic. I put ther fruits/veggies or treats, or toys inside and they go crazy getting them out. I'll attach a picture of that to show you.
Besides that, it's up in the air what they'll like. My little girls likes hanging fleece ropes but my boys like branches better. Just experiment and I'm sure you'll find some great things. Try baby toys too. One one of my boys just loved this doll house I had and he would go in through the door and to the different levels. <img src="/ubbthreads/images/graemlins/heartpump.gif" alt="" />