Marxists Internet Archive
Marxists.org: "Existence and Being" by Martin Heidegger
One of Heidegger's works that is "easier" to read. Does require some background information, but a good way to introduce one's self to Heidegger and his peculiar writing style.
Other
The Case of Martin Heidegger, Part Three
The third and final part of this excellent series on Heidegger's Nazi involvement.