@dc10 , some of the things I blend into smoothies to make them healthier (and still not too bulky) are Greek yogurt, protein powder, spinach, tofu, flax meal (for fiber that is, again, not too chunky), and occasionally a little peanut butter (although I'm more careful with that, as it's a little harder to digest, I think). I have a bunch of different kinds of frozen fruit that I can throw in, too.
I also use different kinds of milk--cow, soy, almond, and coconut--at different times, because they all have different nutritional benefits.