Eat a balanced meal 1.5-2.5 hours before ride, 45 minutes into ride, pop a gel. If the ride is 70+ miles long I'll have a second one at 50-60 miles in.
I also drink PowerBar Endurance, though I am experimenting with Clif Shot.

On MTB rides, I eat Clif Bars and gel since I find that it helps me keep my focus better, wheras in road cycling I'm going 2-3 times faster and don't need as much focus and handling skills.

::EDIT:: Personally, I've used all 3 PowerBar gels, as well as Hammer, Honey Stinger and Clif. Clif Shot is the best, with PowerBar 2x Caffeine in second, and Honey Stinger in third in terms of best performance.