TheUpanishads

EknathEaswaran does a good translation.

TheBhagavadGita

EknathEaswaran does a good translation, as well as his series BhagavadGitaForDailyLiving.

GospelOfSriRamakrishna

The teachings of SriRamakrishna, a disciple of whom was SwamiVivekananda.

TheCompleteWorksOfSwamiVivekananda

This set of 8 volumes is available from Amazon, and contains a wealth of useful stuff to read about VedantaPhilosophy

TheSermonOnTheMountAccordingToVedanta

This is a book by SwamiPrabhavananda, another follower of the tradition set up by SwamiVivekananda, following the teachings of SriRamakrishna. It gives a great example of how followers of one SpiritualTradition should view the teachings of another.