Jason definitely has the right idea if you're pinching your pennies.  Hopefully he'll post some pictures for us.

If you're not as handy as Jason though- 

In addition to tre-piu  mentioned above (same company as poliform)- these are some sexy beasts:
http://www.lualdiporte.com/

If you order a simple finish without too many options you can get lualdi for ~$600 per door including the hardware (I've been told).  If you factor in the doors, hardware, jambs, veneer and labor- Jason's technique probably isn't a whole lot less.

Not only do they look incredible but they operate like the door of a mercedes (or other high end german car)-  Since the whole unit is factory fabricated they install and operate like nothing you've ever felt (unless you spend some time in europe where the approach is typical).

For exterior doors, there is an option that is fairly inexpensive.

Attached is a picture of a 3' 6" steel door with some 15" glass panels inserted. This type of window does have a moulding on the inside and outside that holds it in place. The door was made by Masonite and we specified the size and placement of the windows. It was purchased through the local lumber company for $350.

So, you could have just about anything you want made as long as your design does not weaken the structure of the door.

John

PS: sorry for the low res image

I can't believe everybody forgot the obvious one - SIMPSON.

They have from the traditional BLAH to the modern, clean, wood frames. I haven't checked on prices, but I'd bet my dog it isn't an arm and a leg like those foreign makes.

You can also try MODERNUS doors. They are worth the money, I used them myself and I am really happy.

http://www.modernus.com