Can I get some recommendations for manga featuring male masturbation? I was super happy to find the category, but it is so hard filtering out all the other stuff.

This one might fit

Koibito wa Hatsujouki especially stories 3 & 4

I too like stories featuring male masturbation, but most of the time it doesn't really happen when too often.

Onani Master Kurosawa is pretty much devoted to this topic and quite popular, too. I haven't read it myself because it's not at all my thing, but the comments and ratings are very favourable.

I don't know if these suit your taste but they're quite good read anyway and featured male masturbation:
Sundome (quite frequently in this one)
Ore no Himekutsu o Haite Kure
Satanic Sweet

DONDAKEE!!