Depending on how large your site is, my first recommendation would be for an online creator at xml-sitemaps. They have both the ability to have your site spidered (up to 500 pages if I remember correctly) for free or a script that you can purchase and install… obviously this may vary depending on your level of hosting and control. The paid version would not have the same size limitations and one of the benefits is that you can setup patterns to avoid including duplication or sections that you don’t want spiders to crawl (though you’ll still need to use robots.txt or meta tags to fully block the spiders on these pages).

From there, WebCEO, which is downloadable and runs from your computer, just added the ability to create XML sitemaps. However, unless you intend to use other features of WebCEO, I’d lean toward the first option.