You forgot...
-kids (unless they're teenagers making the wheelie gesture... I flip them off)
-horse and buggies (yes, the Amish will wave back)
-people mowing the lawn
-people checking their mail
-classic cars
-and I'm sure I forgot a few too
I try to wave to everyone. My favorite is people who don't wave back. That puts a huge grin on my face. It's mostly Harley riders wearing fake helmets. The guys without helmets usually wave, as well as those with DOT helmets. Most sport bike riders start to wave to me from quite a ways out. I rarely get to initiate. I typically initiate with cruisers (which far outnumber sport bikes in my parts). Sport tourers, standards, and dual-sports (anything with an upright riding position) seem to be on my same wavelength. We seem to wave right about the same time. It must be some sort of cosmic thing.
And if you're passing a horse and buggy going the same direction, it's courteous to clutch in and let the RPMs fall to idle as you coast by. The horses appreciate that. If you ride by like a squid, they'll sh!t in all the good corners.