Today the Orthodox Church also celebrates the memory of two great ascetic Fathers, Saints Isaac and Ephraim the Syrians. A good number of valuable resources about these saints can be found online, for which I'll provide a brief guide.
An excellent sermon on St Isaac, giving an overview of his life and teachings, can be found here. Excerpts from an essay by Fr Justin Popovic on St Isaac's theory of knowledge can be read here. This link leads to a selection of brief excerpts from the saints writings; here is a series of his aphorisms. Here is a lecture by Bishop Hilarion (Alfeyev) on St Isaac's teaching on prayer. Finally, this website is entirely dedicated to St Isaac.
Turning to St Ephraim the Syrian, one can find a brief introduction to his works here, with links to translations of his writings on the upper left. A short life of St Ephraim is here. This link leads to the liturgical service in his honor. A very good selection of links (a few of which are dead, unfortunately) can be found here. Finally, a succinct academic study of St Ephraim can be read here.
Here is St Ephraim's spiritual testimony, which all who honor his memory would do well to heed:
I Ephrem am dying and writing my Testament,
To be a witness for the pupils who come after me:
Be constantly praying, day and night;
As a ploughman who ploughs again and again,
Whose work is admirable.
Do not be like the lazy ones in whose fields thorns grow.
Be constantly praying, for he who adores prayer
Will find help in both worlds.
The icon above depicts the burial of St Ephraim.