This isn't exactly what you asked for, but the three biggest factors that alter libido: diet, exercise, and stress.
Diet:
+ Cut back on sugar, simple carbs, and alcohol. These all cause spikes in your insulin levels that can kill libido.
+ Eat more raw fruits and vegetables. There are a number of enzymes present in fruits and veggies that stimulate beta-endorphin and dopamine production (two things that make you feel good and "in the mood"), however most of them are destroyed when cooked.
+ Drink more water and/or electrolytes. Dehydration and electrolyte deficiency both put stress on the body that will inhibit arousal. If you find yourself "out of sorts" at the end of the day, try downing a Gatorade or a big glass of water and see how you feel in 15-30 minutes.
Exercise:
+ Stimulates a healthy metabolism, which keeps insulin levels in check.
+ Stimulates endorphin production to give you that feel good high.
+ Improves blood flow to the important areas.
Stress:
+ Biggest libido killer for men. Nothing will help in any permanent fashion until you bring your stress levels down. Sex and stress just don't work together.
Its not a magic pill, but I hope this helps anyway.