Walter Koenig wrote a book too.
Wlater Koenig also wrote comics.
For that matter, Tekno Comics published Leonard Nimoy's Primortals, he's credited with the plots, but I have no idea how much writing he actually did.
Mark Lenard (Sarek) wrote Malibu's Star Trek: Deep Space Nine, The Celebrity Series: Blood and Honor comic.
Aron Eisenberg (Nog) also wrote one, although I'm not sure if this thread is for just Classic Trek actors or not.
Thanks for the info, Keith. I wasn't aware of those that you mentioned.