I second the milk rings! Nova loves hers; we have 1-2 dozen... mostly under the stove and refrigerator! 
Da Bird. It's a wand toy that you hold and wave around, but it's different from the other wand toys that are out there! The feathers kind of flutter (like a real bird ?).
Squishy balls they sell at PetSmart (they have kind of a spongy texture, and are sold in a pack of 4). They sell something similar at Petco, but the ones at Petco have these annoying seams in the middle. One of our cats likes to fetch them, but the others like to bat them around.
Another favorite is the Yeowww! Catnip Pollock.
They also enjoy munching on cat grass.
If you have time to supervise their play, some of the human toys that have interested ours include bubbles (they are mesmerized by these for much longer than I can actually blow them) and ZhuZhu pets (be careful that their fur doesn't catch in the wheels!).
One of our cats loves to look out the window. We bought a couple of those LazyPet window perches, and put a bird feeder up outside.
Another thing they really like are these pop-up cloth cubes they sell at Walmart for about $4 each. They come in red and purple, and maybe other colors too. The cats hide in them when they're chasing each other, and they also take naps in them.
We have 4 cats and they don't go out, so we have a big variety of toys and cat furniture. (Two cat trees, several cat beds, several play cubes, and a whole box full of toys). They really like to play in paper bags, and cardboard boxes, and their cat trees.
Your eight month old might calm down a little bit as he gets older. I've fostered some kittens/young cats that made my 4 look mellow in comparison! 
I've also noticed that some toys are popular for a little bit, aren't played with in a long while, and are popular again months later. Try hiding some of their toys and then bringing them back out later.