WordPress For Dummies, 3rd Edition
recommends one of the most popular WordPress Plug-ins: Google XML Sitemaps, which has been been download 5,177,093 times as of this writing.

This must-have plug-in can build site maps for the robots of Google, Yahoo! and Bing and notify these search engine whenever you post new contents to your WordPress sites. For example, WP89.com site maps is at https://wp89.com/learn/sitemap.xml , generated with the great plugin.

You may find more details of Google XML Sitemaps at:http://wordpress.org/extend/plugins/google-sitemap-generator/ and this video tutorial on Youtube:
http://www.youtube.com/watch?v=G8k3onLrWdc