1. Craft store feathers. Cheap and not terribly effective, but do pretty well between toes and directly in the navel. Are pretty much destroyed after one use but are super cheap so they're nice to have.
2. Feather duster. See above, generally not very good for anything besides teasing, though some say it's very relaxing so I use it as a cool down toy.
3. Backscratcher. A killer, generally the most effective thing I use aside from fingers. Cheap and available anywhere, the "bear claw" design pictured is pretty much the GOAT as far as scratchers go, though I've seen
the wooden "sled" shaped ones in videos get pretty good reactions as well.
4. Wartenburg wheel. Another one of the best things around, the one I have is exceptionally sharp. People recommend dulling them down against a table or the floor but I prefer to keep it spiky and just use it very gently, as the combination of sensations is always considered one of the weirdest and most fun. Very cheap on Amazon and eBay and highly recommended.
5. Nylon braided rope. Best multi-tool, the nylon makes it feel incredibly comfortable against skin and can be used to tightly bind someone with the maximum comfort, and the plastic-feeling texture of the rope works great between toes for reactions. Can find a lot of it at any Walmart or home improvement store and I can't recommend it enough.
6. Hairbrush. Everyone knows what these do.
7. Make-up brush. A very soft tool to use for cool down breaks similar to the feather duster, it generally elicits more of a giggly reaction. I've had people say it turns them on. Get one.
8. Barber brush. Pretty much like the make-up brush, but tickles more. Think of it as a big paintbrush.
I also have a variety of paintbrushes too, but each do some variant of another tool listed above and they're not worth mentioning in specifics.