A few years ago I taught a class on "Opus Teutonicum", a medieval form of embroidery popular in the Germanies in the 13th and 14th centuries. This is essentially the handout I provided for that class.

It is worked on white linen with white linen thread, making it difficult to photograph well, but it's actually not at all difficult to do.

There's also a good basic article on this style here. This handout gives some examples and patterns.

Click on each page to see a larger version.