Their shakes have been around for quite some time with the usual chocolate, vanilla, and strawberry (strawberry being the best in my humble opinion) always available and with specialty flavors such as orange cream, very berry, Neapolitan appearing from time to time. Longtime Del Taco fans will remember that orange used to be a permanent choice and people still often search for "del taco orange shake."
I've had the strawberry lemonade a few times in test stores and it is now available at all locations. So when you go to Del Taco keep in mind that there are many beverage options available.
Read about their other new menu items (the chewable kind, not the drinkable kind) by clicking here then scrolling down a bit. If I even mention what they are in this entry it'll get the search engines all confused so be adventurous and give it a little click.