SitemapXML (http://sitemapxml.net) is a Web-based tool made by Hiox India that allows users to quickly and easily generate a sitemap without downloading any software. You'll need to enter the URL for your site, the last date it was modified, the frequency at which it changes and an email address if you want to receive the sitemap via email. SitemapXML generates Entensible Markup Language (XML), Resources of a Resource (ROR) and text sitemaps that can be used by a number of different search engines.
One of Lisa's latest articles about Web development on BrightHub. This article lists several tools that you can use to create sitemaps for Google and other search engines.