Besides fueling up on caffeine, what can I do to stay more awake and alert?

I'm having one of those horrible lazy lethargic days. My mind and body feel numb and depleted, even though I had a good night's 7 hour sleep and had a hearty breakfast of coffee, omelet and fruit. I've been exercising regularly but not excessively so. What other measures can I take to make my brain focused and attentive?