Well... I am not huge on added powders or anything like that (certainly not protein powders), but there is one I've been using lately. Brand is HealthForce Superfoods, and it's called Vitamineral Green. It's a combo of dried, powdered nutrient rich foods like Kelp, wheat grass, ginger and such. See if you can find some.
I do add a little frozen, chopped spinach to my smoothies (you can't taste it) and also on occasion, when I really need "staying power," I soak 1/4 cup of almonds in water overnight and then the next day, drain them and add, and then I also will add about 1/3 cup rolled oats (you have to blend for a few minutes for it not to taste gritty). The almonds provide a shot of protein and natural fat, the oats are complex carbs, neither one costs a fortune, they are both completely natural. But it makes a very filling smoothie!!