The most consistent part of our Saxon heritage are the fortified churches that you can find overall in Sibiu, Mureş and Braşov county. Some of them I've visited myself and these are:
Biertan - the most famous one, we already have a post about it here:
Moşna - unfortunately this one was closed so I had to admire it only from outside:
Stejăriş - small but neat, it currently undergoes a massive restoration process:
Richiş - not fortified, but full of history, you can learn here about the misterious Green Man:
There is an excellent website dedicated to these monuments: