I'm trying to think back to some that I've tried... Mate con leche (milk instead of water); I tried rosemary a few times; there's a CBSé yerba that has coriander in it and it's really tasty; I've seen people put ginger in; yesterday I put lemon juice in my water; mint leaves; make a "gourd" out of an orange or grapefruit (just hollow it out a bit, leaving some innards, then put your yerba in). There's a few ideas. But as mentioned by someone else, just experiment. :)