C-Span is offering educators tools for helping students understand the electoral college process in its The Electoral College and the Constitution lesson plan. All tools are free downloads.
2012 Electoral Map
Electoral College History
Very nice chart showing modern electoral college results from 1900-2008. These results are also compared to the popular vote.
2012 Electoral College Map Activity Questions
Opened ended research to spur thinking.
You may also be interested in their Campaign 2016 page.
Presidential Elections in the United States: A Primer
Very long and detailed accounting of the entire process, from beginning to end from the Congressional Research Service and the Library of Congress.
The Constitution on the Election of President
Summary of relevant constitutional passages.
U.S. Code: Election Law
Summary of relevant passages.
What is the Electoral College?
Summary from U.S. National Archives & Records Administration.
Electoral College FAQs
Frequently asked questions from U.S. National Archives & Records Administration.
270 to Win
Interactive electoral college map for years past and present.