There are a number of free tools that help you create a Google sitemap:
Google Sitemap Generator made with Java!
Google Sitemap Generator made with a Python script
Open Source Sitemap Script
Google Sitemap Generator and Editor
Google Sitemap Generator for Windows
Google Sitemap Generator Dreamweaver Extension
Arne Brachhold’s WordPress plugin creates a new XML sitemap for your WordPress blog. The donation ware plug-in makes it simple to generate a sitemap. A few minutes invested in creating a sitemap could make a significant difference in your blog’s rank, positioning and traffic.