I also use soy powder. The trick here is to add it at the last minute and barely blend it. If you overblend the soy powder you get a big gloppy mess.
I've also added a dash of flaxseed oil that I just happened to have on hand. Sounds gross, but you'd never even know it was there as long as you don't' go overboard.
While we're talking about smoothies -- I take my ripe bannanas, peel them and wrap in plastic wrap and freeze. They may turn a litttle brown after a few weeks, but are still delicious and make extra thick frozen smoothies. My favorite is: 3/4 cup rice/soy milk 1/2 or 1 whole frozen bannana 1/2 cup blueberries - fresh or frozen 1/2 tsp vanilla extract Whir all in blender until smooth
Sr. Academic Technology Development Analyst
Information Technology Services
Saint Louis University