I've been struggling with this for years, and the only thing I've found that works when nothing else does is hard exercise. The other two things that I've found help the most:

• Let the sun hit your eyelids first thing in the morning (to halt melatonin production)
• F.lux, a program that auto-adjusts your monitor's light levels (and keep your room lights low at night; otherwise melatonin production will be delayed)

EDIT: Apparently keeping your room lights at a low color temperature (incandescent/halogen instead of fluorescent) is better than keeping them at low intensity:

"...we surmise that the effect of color temperature is greater than that of illuminance in an ordinary residential bedroom or similar environment where a lowering of physiological activity is desirable, and we therefore find the use of low color temperature illumination more important than the reduction of illuminance. Subjective drowsiness results also indicate that reduction of illuminance without reduction of color temperature should be avoided." —Noguchi and Sakaguchi, 1999 (note that these are commercial researchers at Matsushita, which makes low-color-temperature fluorescents)