Chamomile works surprisingly well I usually drink a cup at the end of the day to wind me down.
Frankly, I think almost anything you drink hot or warm that isn't coffee will relax you somewhat. I remember when I was a kid and we used to drink warm water pretending it was tea and I would get that same calm feeling (although very mild) that I get when I drink herbal tea. Technically, warm milk might do almost as well (though the effect will likely wear off as soon as your body temp goes back to normal).
I had some Celestial Seasonings chamomile tea but I drank the last of it a few days ago. They have a lot of different flavors. I didn't care much for the one I had. It was honey lemon or something. Their "sleepytime" tea is probably more effective but I've never tried it. Bengal Spice also gives me a nice calm.