Google site maps

I was reading this codex link about google sitemaps:
http://codex.wordpress.org/Search_Engine_Optimization_for_Wordpress#Google_Sitemaps

Since members are telling me that I have a custom permalink structure in which my individual posts are not ranked by google, I’m guessing it’d be a good idea to give google as many alternative ways of getting my site information as possible.

A google sitemap sounded like a good idea. There are a lot of links in the codex article to plugins that help generate such a map. Can anyone tell me which one/s they like.

Also, do you think the sitemap really helps?