I wasn’t able to find a website with a triad color scheme, but did for the others.
Monochromatic
www.target.com uses a combination of red, white and black (I like the way this looks)
Complementary
www.ufl.edu and www.denverbroncos.com uses a combination of orange and blue
www.modestmousemusic.com uses a combination of pink and green in their message board (I wouldn’t normally put these two colors together but this seems to work)
www.panera.com (uses green-red and orange-blue for double complementary color scheme)
Analogous
www.gorillaglue.com uses orange, brown and red pretty successfully
www.zeldman.com is also tastefully done
