Message of President Polk to Congress of May 11, 1846, can be found at http://www.dmwv.org/mexwar/documents/polk.htm.
Pictures and political cartoons were found at http://www.humanities-interactive.org/invasionyanqui/
http://www.boondocksnet.com/cartoons/mcc085.html - Contains various political cartoons from the Mexican American War along with other 19th century events.
http://www.pbs.org/kera/usmexicanwar/ - A PBS site that contains various biographical articles and history of the Mexican American War.
Armento, Beverly et.al. America Will Be, Houghton Mifflin Co., Boston, 2000.
PBS presentation of The Mexican American War 1846-1848.
http://www.lsjunction.com/people The Lone Star Junction site, which provides many 1 page biographies with pictures of Americans involved in the war.
I found none of these dealing with the Mexican American War.