As someone who cannot have sugar products (due to an RNY gastric bypass procedure, not diabetes or anything) and tried live tests on everything: Never had issues with splenda. (Not saying others don't.) It's the Maltitol and other "sugar alchohols" that get you. Xylitol might be an option, but not if you share your beverages with your dog.
Nick, the Crystal Light teas are awesome. Powdered, but awesome. I am completely taken with the blueberry white tea (only comes in those stupid little On the Go packs, but the taste is worth it. Dump one in a liter of water and I am good to go.) And Lipton makes some unsweetened teas in a bottle. So do a few other companies. check the beverage aisle in your local grocery. If you have a Trader Joe's in your neigh borhood, try there, I KNOW they have it. You can even get a quart bottle for those really desperate moments.
If you like pop, you might also consider Diet Rite and the Hansens brands. Hansen's makes a no sugar ginger ale that is dry, crisp, and is so gingery it will make you sneeze.
Good luck finding a solution.