I've tried chai in Berkeley, Santa Cruz, San Diego, and Boston, and so far the absolute best, smoothest, most heavenly cup of chai has been at a small coffee shop in Ocean Beach, San Diego, CA. It's on Newport, called Jungle Java (I think). They have one of the best spice mixtures I have ever tried, and the place is really nice for sipping it, too. I ask every time where they get it, and they don't know, but I will find out one day... (Be sure they make it with milk! Some people apparently ask for it without and they make it that way if you don't ask for it.)
Also, the Oregon chai is pretty good, I think, but a little too sweet for my taste...