Soaked cashews, blended with water, vinegar, and lemon juice is a recipe for a sour cream... I find the texture a bit off, so I mix it 50/50 with mayo for the base of my dip or plain as our sour cream. Everyone that has tried it really likes it. Another option is mixing 50/50 yogurt substitute with mayo/veganaise. I haven't found a good substitute for cream cheese (we avoid soy, so that's out) so I'll be
for that.