I think one of the lowest calorie ones out there are Syntrax nectar, and the nutrition profile looks good - but honestly, I hate them. They're a fan favorite, though!
Premier RTD shakes are the ones I used the most. 30 grams of Protein for a container, and they kind of taste like Yoo-Hoo to me. Plus they're easy to stash all over the place so there's always one handy.
Syntrax Matrix is pretty good, but check to make sure it's on the approved list for your program. It was on ours, but I've seen a few people say it isn't on theirs. Good protein, decent taste, and the price is pretty good too.
In terms of taste, BSN Syntha-6 is probably my favorite. It IS a little higher on the calorie side, but I don't use a full serving at one time. I worried a lot about the calories in that one (200/serving) at first, but it turns out I can't finish a serving, so it's a moot point.
Check out places like Nashua Nutrition (there are others, too, I just can't think of them) and you can order samples of a whole bunch of brands and flavors for less than $2 each. Good luck finding the right one!