Chili Peppers are known to help keep blood flowing freely which helps lower the risk of heart attack and stroke. They help the body to dissolve fibrin, which is a substance necessary to the formation of blood clots.
They contain a substance called capsaicin, which fights inflammation. It is currently being studied for pain relief such as in arthritis and psoriasis. Capsaicin also helps fight diabetic neuropathy and helps clear mucus from congested lungs.
One more thing about capsaicin - in cancer research studies, they have been shown to stop the spread of prostate cancer cells.
Many athletes advocate using chili pepper sauce on foods to speed up metabolism. It does this by increasing your body's heat production, which also causes a need to use more energy (calories).
Don't worry about the heat - they won't cause stomach ulcers. Chili peppers actually kill harmful bacteria from other foods you may have ingested and stimulate cells that line the stomach to secrete protective juices.