For me it's the third eye, I just feel a kind of "electricity" in my forehead area. Happens to me whenever I feel relaxed, or if I focus on that feeling/area. I was going to post some youtube videos, but for some reason my browser is acting up. Just search youtube for "chakras" and you'll get tons of stuff.
EDIT: Ok I got youtube to listen to me, I really like this video about chakras. It gives a good general overview on them.
YouTube - The Illuminated Chakras by Anodea Judith ® Pt. 1
-Andy
