The Welsh Triads
Llyfr Coch Hergest
The triads that were presented here were from Rachel Bromwich's book Trioedd Ynys Prydein; it is a monumental work, and since it is now back in print (it was out of print and impossible to find for decades) and updated, I suggest purchasing the book--though expensive, it's worth every penny, being some 600 pages long. I recently received my copy, and I can't express how fantastic the book is.
Still, since the text is now more readily available, I am taking down the triads which are translated by Bromwich; at some point, I hope to do a translation for this website, but that's will take some time as I'm still a novice when it comes to Middle Welsh.
I will, however, finish the diplomatic edition of Rhys and Evans, which has been started here.