I'd make #1 the printing press, although it could be argued that the Chinese invented it much earlier.

I wouldn't make printing the #1 but it should be in there...
and what about the phone? shouldn't the best of the millenium be the ones that then gave way to a lot of innovations?

refrigeration should be in this list. it's often overlooked but has on important wide-ranging effect on our quality of life. It's not just about your fridge, it's about a large part of our food supply and other perishibles and is argueably the most important factor in the improvement of general health and longevity. Remember at the turn of the 20th century before widespread refigeration the average lifespan in the US was less than 50 years.

There are a few omissions that should be there.
The telegraph is one of them. It marked of the beginning of all electronic communications methods.
Radio is another. It was the first real time communicator.
It is the originating discovery that leads to others.
Take the WWW rating for example. The invention should have been TCP/IP protocol without which there would not be an internet.
The Combustion engine is also missing. It change civilization and the way cities were designed.
So my pick would be those creations that changed mankind forever.

Good grief!

Most of the things mentioned couldn't even exist if we didn't have electricity. Harnessing electricity has to be far more important than a Pet Scan.

As for the calendar being number one, I can't see it. Actually from what I have seen over my mere 58 years, it seems that either the calendar or our seasons are terribly in error. I'd say one of them is off by at least a month!