Well, if you workout at all, pre-workouts are definitely the way to go. 1 scoop of a nice pre-workout can be around 400mg of caffeine, and help you in your workout. Some people buy these without the intent of working out though.. which is a little weird but there isn't any negative aspects of drinking them without working out.
GNC/Nutrishop/Nutrizone's should carry them, just ask for pre-workout supplements, or you can probably order them from Amazon. This is what I use (all though i actually lift weights)
Alternatively, you can waste $ on energy drinks (less bang for your buck, but convenient)