The database called LexisNexis Academic (third on this list: http://library.unomaha.edu/research/topten.php) is the most wide-ranging and the best place to start. If you need older articles - say, more than 20 years old - the New York Times has a database containing their entire run from 1851 to 2009. You can find it by selecting "N" on this page: http://libguides.unomaha.edu/A-ZList.
