The Heart of Compassion: The Thirty-seven Verses on the Practice of a Bodhisattva with the commentary of Dilgo Khyentse, is another essential work for aspiring bodhisattvas.
The root text of the 37 verses is by the Tibetan bodhisattva Gyalse Thogme(1295-1369). Several other translations with commentaries exist, but this is one of the most inspiring.
Two other excellent commentaries on the 37 verses are
Transforming the Heart by Geshe Jampa Tegchok and
Keys to Great Enlightenment by Geshe Tsultim Gyeltsen. The latter title can be had for free when ordering something else from Snow Lion publications. It also contains another important text that HH Dalai Lama likes a lot;
Eight Verses of Thought Training by Kadam Geshe Langri Tangpa.
http://www.snowlionpub.com/search.php?isbn=KEGRENThe root text is online here:
http://www.indianabuddhist.org/37Practices.pdf