We have used Undercover Tourists to order our tickets, and they are great. We got our tickets a couple of months ago for our October trip, and they even sent a photocopy of the tickets which was a nice touch!
They provide great customer service, too. I made a mistake in my order, and when I realized it, I called them. They were able to make the correction and credited my credit card, and it all turned out fine.
I'm getting ready to order Blue Man Group tickets through them soon!