Apple - There's Fanta Green Apple, which is fairly good, and Mountain Dew Thrashin' Apple, which is horrid, though I maintain that "dnL" is still the most disgustingly sweet soda I've ever tried. There's also the Jones Soda Co., but they're only good for their Pineapple Cream flavor.
Crystal Pepsi - Was probably just a marketing gimmick, really. Homer Simpson going "mmmm, invisible cola" was a good gag though.
Cinnamon Coke was a holiday thing and may come back. If it does, sign me UP! There's a new Gingerbread Mountain Dew this week that is probably horrible.
I've had the Walmart brand sparkling waters...they could have been worse, I guess, but I prefer Sparkling Ice for that sort of thing.
Really I can't taste the difference between most of ANY lemon/lime sodas. I'd probably be able to tell 7Up in a taste test but not the others.
Dr. Pepper Vanilla Float was okay, but discontinued and Dr. Pepper & Cream Soda has destroyed it probably. I hope DP&CS is here to stay, for I loves it. I just had some, while watching Come And See!!