These are always interesting threads. I work with a relatively large variety as well, though not as many as Dario and still probably fewer than the number of concave cutters, Chinese or otherwise, that he has
Maples - Trident and Japanese (green leaf, red leaf, cork bark, ao kanzashi, kotohime, shishigashira, chisio improved, katsura, coral bark)
Hornbeams - Korean and American
Elms - Cedar, Chinese cork barks (standard, Seiju, Yatsubusa), American, Zelkova
Pines - JBP and Ponderosa
Oak - Willow and Cork
Juniper (Shimpaku, Kishu, Itoigawa), Bald Cypress, Wisteria, Yew, Boxwood, Spruce (Engelmann), Boulevard Cypress
Other species that I've started (mostly in the ground) over the last year or two from seedlings (mostly from Brent) just to play around with to make shohin out of: Stewartia, Prunus (crab apples, ume, flowering cherry, flowering pear), Flowering quince (too numerous to name), Styrax, Cedar (Atlas)
I've dabbled in other species, but recently gave up beech and azaleas, as they would inexplicably die on me (thankfully on the azaleas, I started off with relatively inexpensive stock). I've had bouts of verticillium wilt problems on a few japanese maples, so I don't think I'm going to push any further into them.
Over time, I can see myself further whittling down my collection and really focusing on tridents, elms, japanese black pine, hornbeams, bald cypress, yew, junipers, and spruce, as these are species that even I have a hard time killing. And then of course, some of the other species as more one- or two-offs. I like the variety and having different tasks over the course of the year like someone else mentioned.