Capsaicin

According to 'Science and Lore of the Kitchen' by Harold McGee, researchers have isolated five capsaicinoid components that have different effects on the mouth. Three give 'rapid bite sensations' in the back of the palate and throat, and the other two a long, low intensity bite on the tongue and mid-palate. Capsaicin accumulates in the fruit concurrently with the pigment during ripening and is primarily found in the white placental tissue to which the seeds are attached. So you can moderate the heat by scraping away all the white bits.
This year my peppers have grown really well, much better than anything else. The two smallest are the most fiery - Gelbe Kirschen & Pretty in Purple. These are really very attractive plants, small and bushy and covered with fruit, but they are fiddly to prepare. Doe Hill is sweet and the other two are mildly spicy. (The slate is ruled in one inch squares.)