I have a few recommendations of my own to add to the list.

• Feed Control is a plugin that lets you add your WordPress pages to your RSS feed, and will also allow you to remove pages or posts from your feed.
• Sitemap Generator is a good tool for providing a site map to your visitors.
• Order Pages is a plugin that allows you to easily and visually arrange the order of your pages in navigation bars and menus — you can certainly edit the “page order” number by hand for each page but if you have a lot of pages this makes ordering those pages a breeze. And the My Page Order plugin can do this well also.
• Category Order — while the above plugin arranges the order of your “pages”, this plugin arranges the order of your blog “categories” — which is handy if you are using your blog categories in an unusual way while using WordPress as a CMS — Category Order can be found near the bottom of the linked page here.

Update: Here is a great list that contains some very helpful plugins for leveraging WordPress as a CMS — Top 10 WordPress CMS Plugins at Blueprint Design Studio.

Update: (Friday; April 11, 2008) — Obfuscate E-mail is a plugin I find I need on most WordPress powered sites I setup — you can post email addresses as links and this plugin will obscure the address in the html so as to confuse spammer bots.

Update: (Tuesday; May 6, 2008) — the Role Manager plugin gives fine control over which users have access to what features on your WordPress install.

Update: (Tuesday; October 21, 2008) — Search Unleashed – Advanced WordPress searches with highlighting as well as searching of pages and posts.