One of the most ubiquitous of mixers, Coca-Cola is a staple in most bars. Unfortunately, it is almost always on a soda gun which it shares with other sodas and juices. A few bars will still pour Coke out of a can or bottle. This is an improvement, but the best Coke comes from a glass bottle and uses sugar not corn syrup.
Originally, Coke was made with sugar. A few decades ago, they started using corn syrup because it is cheaper. The original Coke with sugar really does taste better. You can find it in glass bottles in hispanic food stores or in the hispanic section of Wal-Mart.
Try the good stuff in a Cuba Libre--it really makes a better drink.