WriteMaps is a useful site where you can create sitemaps online. I was actually looking for something like this the other day when I was creating a content inventory for a client. Unfortunately, WriteMaps is lacking in the feature department: you can’t yet share the sitemaps, as they say on their site, but that is coming soon, and you can’t import/export sitemaps. Still pretty useful if you just want to organize a sitemap right away.