Here is an open source sitemap generator from Google:
http://code.google.com/p/googlesitemapgenerator/
Also, if you just search for "Sitemap Generator," there's a ton out there. Many are free for smaller websites and inexpensive for larger ones. Most CMS software can generate its own sitemap, too.
You can find a new version of the XML -> OmniGraffle script on my site at
http://nik.me/crappysoftware .