There's a lot of things you can put into pepper mills.
Although I have quite a collection, I usually just fill my pepper mills with white and black pepper. That's two different pepper mills ...
... sometimes, though, I mix all the various round seeds off my spice shelf and throw that into one or the other peppermill. That makes for a more interesting taste:
Pic: Black pepper (Piper nigrum), ripe.
Pic: White pepper (Piper nigrum), ripe and stripped.
Pic: Green pepper (Piper nigrum), unripe.
Pic: Rose pepper (Schinus terebinthifolius), also called Brazilian pepper.
Pic: Sichuan pepper (Zanthoxylum acanthopodium), also called anise pepper ... this is one of those seeds that'll completely numb your tongue, if you chew on the seeds fresh off a tree.
Pic: Allspice (Pimenta dioica), also called clover pepper.
Pic: Coriander (Coriandrum sativum), included because the seeds are the right size.
Pic: All of the above. Pretty, no?
And I forgot all about chasteberry or monk's pepper (Vitex agnus-castus), cos that one is not on my spice shelf. Thus there's no photo of that one, sorry.
And a search of my site for "pepper" gives lots and lots of peppers which I don't have yet ...
... hint, hint.