I discovered this about a week ago and it frankly surprised me. Apparently the Robots.txt file has a new agreed upon protocol for implementing sitemaps
To simply add a sitemap to your robots.txt file simple open it in a text editor and input the following example:
SITEMAP: http://www.(yourURL).com/(yoursitemap).xml
That's it. By adding this code to your Robots.txt you have allowed all major search engines, Google, Yahoo, MSN, and Ask.com, and minor ones, the ability to see your sitemap and properly index your website according to your choices.