I am looking for a product that will wirelessly broadcast a streaming
video signal to multiple monitors/displays at once. There will be one
output and multiple inputs.

For example, one possible scenario is there is a computer downstairs
that will play a DVD, and I will have 4 monitors upstairs that will
display what is showing downstairs.

There is a space constraint, so the less equipment used (with the
displays), the better.  The displays will most likely be LCD Displays.
Attaching a computer to the displays is not an option.  The solutions
must be reliable because the video might display for several (10+)
hours at a time, and the wireless signal must go through walls.

Please provide some possible solutions.  We are looking for the most
reliable, cost effective solutions.

Wireless and reliable aren't always exactly compatible terms :) 

If money weren't an object, how about all-in-one computers like
http://www.tekpanel.com/flat-screen-monitor.html :) (about $6500+
each)

I know that's not what you're about. Check out a froogle search for
Wireless Video Sender...
http://zalmar.com/itemlist-Video-A_V_Accessories-Audio_Video_Signal_Sender.htm
is probably where you can find exactly what you need. One sender,
multiple receivers.

Multicast! Setup a multicast server on a server in the basement and
have small machines hooked up to the displays to recieve the signal
and display it. That doesn't have to be a fullsize desktop, they make
very small pcs that attach to the back of LCD displays, or a small
handheld might even work.

There is an opensource Multicast package called VideoLAN. Works great,
but make sure that if you're using it via wireless that it's 802.11G
as a streaming DVD stream can be fairly big.

http://www.videolan.org/

forge