OK, here's an overdue but extensive reply/recommendation:
The best toy that my balls have ever experienced is a rubbery, not-originally-intended-for-sex toy that’s sold under a variety of names. But I think the one I bought was called a Super Mondo Ball. Although parents and the toy manufacturer would surely be horrified to hear, this thing gets along GREAT with adult male genitalia. You should be able to find it for under $10 locally at small, independent toy stores.
It's basically a squishy, stretchy ball you can turn inside out through a circular opening. One side is smooth and silky like a tit, and the other has weird, wiggly "tendril" protrusions softly poking out like a sea anemone. And everything about it makes my testicles feel loved.
There’s also a wide range of variations of wrapping the thing around your hands or your dick to stroke your shaft with sensations that are amazing but nothing like a woman. And as such, it's more of an accessory to a Fleshlight or different experience for your dick that is nothing like a Fleshlight.
Some more details:
You don't really need lube because it's so smooth and silky, but a water-based lube can double your range of sensations. Without lube, its stretchy fleshy material has a nice "stickiness" to it so that it clings to itself.
The way the thing is shaped with its opening, it can stretch to wrap around your balls so you're hung like an elephant. But what feels even better is having it wrapped around your entire genital package and cling down there hands-free. It’s great the way it hugs, cock/balls and all, with a gentle downward tug provided by gravity. It feels *awesome* just walking around with it swinging around and hugging and tugging down there on my gear. Since it's stretchy, it will expand to accommodate an erection. However, if you're trying to get it to do this thing to contain both your shaft and your 'nads, it goes on best if you wrap it around everything when your penis is still fairly soft, letting it grow inside.
And, YES, this thing caressing my balls while my cock is shoved into a Fleshlight feels pretty great too.
When reversed so the smooth side is inside and the "tendril" "finger" things are on the outside, gripping the ball causes the "tendrils" to cling together. They'll slowly spread themselves back apart, causing the Mondo Ball to tingle as it pops back into shape. That feels like it's got a life all its own. With the "tendrils" inside, the way they wriggle around your shaft as they separate is also a wild sensation.
Lying on your back with it cupped around your entire package and the smooth side facing out, if you stretch the opening apart and press it against your skin, it shrinks back into place around your manhood with a crazy lifelike slither.
So this thing is like having a little friend that enjoys grabbing your cock and balls. Actually, especially in "tendrils-out mode," it looks rather freaky, as if some weird space creature has attached itself to your crotch to feed off your sexual energy.
With a little water-based lube (or even if you're getting sweaty down there), gravity will pull the Mondo Ball sliding down off your genitals, caressing your package as it moves down. Not a bad thing!!
It can be a bit difficult to explain/picture, so here are some “demonstration” photos: