I'd suggest either cocoa nibs or plain, unsweetened cocoa for smoothies if you want something chocolaty. I don't have a recipe, but I did make a really tasty one with a banana, Silk coconut milk, cocoa nibs, ice and peanut butter. Very tasty!
However, I'm curious what your goal is for smoothies. If you are looking for a lower-calorie meal replacement, or a way to get more fruits and veggies in, peanut butter and chocolate flavors are not going to do much for you.
Personally, I have a smoothie for breakfast almost every day, and try to get 4-5 servings of fruits and veggies in there. This morning was half of a honeydew melon, 3 plums and an apple with an entire bunch of flat leaf parsley, and some liquid stevia for sweetness. This tastes way better than it sounds, and is super nutritious, refreshing, and filling for the calories.
Mostly, I buy what is in season and throw it all together. Right now I have a bunch of cut up pineapple in the freezer ready for my smoothies because pineapples were on sale for $1 each. I also have a bunch of cherries that I pitted and froze, as well as blueberries, since both are in season and therefore cheap. Darker fruits like blueberries and cherries are great in green smoothies that have spinach or kale in them, because they cover up the color, and to a great extent, the flavor of the greens. They also have a big nutritional punch on their own. Another smoothie I like is canned pumpkin with ground flax, cinnamon and lots of pie spices and some milk - tastes like pumpkin pie!
For a liquid, I like the Silk Light Almond Milk, which is about 40 calories per cup, and very neutral-tasting, so it works with most smoothies.