There are three primary sources of coffee flavorings for the average consumer who isn't obsessed enough to roast their own beans: flavored creamers, flavored syrups, and flavored beans.
There are disadvantages to coupling cream with flavor, though. What if you want less cream and more flavor? What if you prefer milk or heavy cream? What if you're one of those people who doesn't like cream at all? What if the taste you're craving isn't among the fairly limited list of flavored creamer choices?
The Syrup Solution
I usually keep a bottle of Torani sugar-free Vanilla in a desk drawer at work, and when I run low I can pick up a new one during a weekly grocery run. I haven't yet tried most of their other flavors; their website claims over 80 syrup varieties, but I've only seen a few locally. The next time I order some flavor syrups online I plan to try a few of theirs, but first I have to finish up the bottles of DaVinci syrups in my pantry. DaVinci sells big bottles of syrup in 60+ flavors, most available in regular or sugar-free.
Another nice thing about these syrups is that they have more uses than just for coffee. For instance, instead of adding sugar or sucralose to a bowl of bran flake cereal, I'll often add a few drops of sugar-free almond syrup. Another combination I like is a little bit of peppermint syrup drizzled over vanilla ice cream.
It's in the Beansnot adding any sugar or calories to your drink.
The tricky part of choosing a bean-based solution is that the ultimate taste of the brew depends heavily on the quality of the beans that go into it, and it's impossible to know ahead of time if you'll like the coffee part of your flavored coffee. With creamer or syrup, you can simply tinker with the brew you already know you like; with a new bean, you're taking a chance.
Don't let that stop you, though! I'm glad I picked up that little bag of pumpkin spice coffee at a local Amish farmer's market last month, and I'll be going back there to try the amaretto soon!