Here's an interesting manufacturer site:
http://www.vectorelect.com/
They have hardware for sale for just about every bus for prototyping and other purposes. They even have three different S-100 prototyping boards. Alas, I have no idea about price and stocking details.
S-100 cards:
http://www.vectorelect.com/Product/P...d/PBSTDBUS.htm
EuroCard selections:
http://www.vectorelect.com/Product/Plugbord/PB3U.htm
These use a standard 96 pin and socket arrangement, and these seem to be popular among the European homebrew crowd. I believe this format was also used for Apple's NuBus implementation.