Chocolate soda (we would have called it tonic here)always seemed like a weird idea to me. I did like YooHoo as a kid, but that seemed more like chocolate milk. Any drink promoted by Yogi Berra gets my vote. Back in about 1985, I remember hearing about Canfield’s Diet Chocolate Fudge soda, from Chicago I think, and it struck me as weird enough that I had to try it. I was stunned; I really liked it. There was no ‘diet’ chemical taste (I will not drink most diet stuff), and it just was tasty. The egg cream idea suggested by berndog makes me want to go and get some now!