This is a fantastic work-in-progress from Virginia Tech that explores the Mexican-American War and the media, which will provide "links to transcriptions of newspaper articles, indexes, images, bibliographies, timelines, and official documents related to the 1846–1848 war between the United States and Mexico."

PBS's site on the "U.S.-Mexican War," includes resources for educators, a timeline, and a series of biographies.

This site on the war developed by Descendants of Mexican-American War Veterans includes maps, documents, and other primary sources, as well as a list of historic sites in Texas, California, New Mexico, Colorado, Louisiana, and Mexico.

You can read "The Mexican War and After," extracted from American Military History: Army Historical Series.

Historical Text Archive; contains some broken links but those functioning include Pres. Polk's War Message to Congress and the text of the Treaty of Guadalupe Hidalgo.