Testicles. Scrotum scrunching can feel very nice. Squeeze and mash upwards against the base of the penis, pull 'em forward, etc. Just as some women like rough action on the breasts and some like a lighter touch and some don’t want any attention there at all, I’m sure there’s a lot of variation amongst us guys w/regards to appreciating this kind of activity, but I’m definitely in the “mash 'em around a bit” category.
It’s obviously in the same general area, but can I help it if we’ve got lots of stuff concentrated in one place?
Kissing during sex is stimulating. Nibbling can be nice. Don’t care for sucking and licking so much. Attention to the boytits does nothing whatsoever for me. I’m just not a breast person in either direction.
What else? Belly-button, oddly enough. Not in isolation from other stimuli, but lots of nerves and old internal connective tissues so that inserting a finger and playing around can feel invasively naughty in a visceral way.