Here's another one: almond and anise seed. You could use either natural almond extract or almond flavored syrup.

Anise seed is not the same thing as either fennel seed or star anise. It's a tiny seed that looks a lot like celery seed. They use it to flavor biscochito (crumbly little cookies) in New Mexico, which is where I got the idea for this flavor combination. I used about 1/4 teaspoon of anise seed for one shake. Start there and then taste before adding more.

I use a high speed blender which obliterates seeds but you could just as well use a spice grinder or mortar and pestle before adding the seeds to the shake. Putting the anise seed in the regular blender isn't going to grind them up.