Wow - you have my admiration for undertaking such a time-consuming task as making tamales by hand! (but it's the holiday thing, no?) Are you vegetarian? Prunes sound great with the masa. You could also, I guess, do a calabacitas-type filling, with zucchini, corn and roasted poblano peppers (sautee with onion and a bit of garlic and cumin, and finish with a dash of cream). I'd personally tend to stick with meat fillings, flavored with ground dried anchos (for a smoky note) or other peppers. You could also do a pumpkinseed, green pepper (roasted and peeled) and sesame seed paste, thin it a bit with cream, and mix it with, say, queso fresco or perhaps pressed extra-firm tofu. Dunno if those suggestions help. Have fun!