It has been proven that Google will spider your site faster if you have a Google Sitemap. In its simplest terms, a Sitemap is a list of the pages on your website. Creating and submitting a Sitemap helps make sure that Google knows about all the pages on your site, including URLs that may not be discoverable by Google’s normal crawling process.
Note: Most of these sitemaps are valid for Yahoo as well!
TOP FREE Online Google Sitemap Generators
3. Sitemaps Pal
4. XMLEcho Sitemap
Other popular Free Sitemap generators are -
Any more to add to the list? Have you used any of these? Which one do you recommend?