Coffee drinkers are nuts for it
Hazelnut is one of the most popular coffee flavorings in the US. There are enough regular hazelnut coffee drinkers that big chains like Wawa and Dunkin Donuts offer it among their selections. But running out to the local convenience store whenever you get a coffee craving can lead to your wallet getting thinner and your body getting thicker - especially if you frequently decide to grab a sugary snack while you're there!
Instead, you can make your own hazelnut coffee at home or the office, flavored exactly the way you like it. Flavor it using syrups or creamers, or brew up a cup using coffee that's been imbued with a hazelnut taste.
Creamers and Syrups
Hazelnut flavored syrups and hazelnut coffee creamers are two common ways to add that rich, nutty taste and amazing aroma to your beverage. Both can be found at many local grocery stores. They're especially convenient if you share a communal coffee pot with unenlightened heathens who have not yet discovered the joys of flavoring; just keep a bottle of creamer or syrup handy to splash a little hazelnuttiness into your drink. I've tried several varieties of both solutions in this kind of situation; they're all good, but in general I prefer the syrups. They allow me to adjust the cream level and the flavor level in my cup independently, they don't need refrigeration like some cream products, and they're more often available in sugar-free versions. I've used both the Torani and Da Vinci brand syrups; both are excellent.
Because hazelnut is such a popular flavor, there's a third option I've not yet tried but am intrigued by: to keep my sugar intake down I use Splenda brand artificial sweetener in my coffee. Splenda now makes flavored sweetener packets, including a hazelnut variety! If I get the chance to sample some of these, I'll report back here.
Nuts for the beans
When I can brew it myself at home (or with a single-serve brewer at the office where I can either bring my own flavored k-cups or convince the boss to order some), I prefer to use flavored beans. These are made by soaking beans in flavored oils just after roasting, and result in a richer, fuller scent and taste than can be had through syrup and cream solutions, and come with the added benefit of not adding any calories or sugar.
Not all beans are the same, of course; the final taste of the coffee will depend on the quality of the bean, the quality and concentration of the oils used, and the soak time. A good way to start if you're considering the flavored-bean solution is to find a brand of coffee you like and see if they have a hazelnut variety. You can buy the beans pre-ground for convenience, but if you're like me you'll get whole beans and use a small electric grinder to fresh-pulverize the exact amount you need for the pot you're about to brew.