Find more than 1 million math equations on the WEB
Springer, one of the largest scientific publishers, has launched LaTeXSearch.com, a free online service which can locate over 1 million LaTeX equations from the mathematics literature.
Try http://www.LaTeXSearch.com --- on the home page, click on one of the "Sample Searches." When the results appear, click on "View LaTeX Code" to see the math markup. You may highlight the markup, and then copy and paste it into your LaTeX documents.