I spent a lot of time trying out various options and a lot of different plugins. The ones listed below are the top 20 plugins that I found nearly indispensable for this particular site, which you can see in action here: Marilyn Fenn Studio.  As always, your mileage may vary.

1. WP CSS Dropdown Menu
   A three-level drop-down menu plugin for WordPress.  It uses Stu Nicholl’s final drop-down code, which is CSS only.  You can modify the style to suit your theme, include a Home page button, and exclude pages from the drop-down menu.  I tried several other promising and not-so-promising options before finding this.  Eureka!
2. Reveal IDs for WP Admin
   In order to exclude pages in the above plugin, you need to know their IDs.  This plugin reveals IDs of pages, posts, tags, and categories, all of which I found very useful in creating the above site.
3. Flexi Pages Widget
   Allows you to choose which of your pages to display in the sidebar, whether to display sub-pages, and in what order to display the pages.
4. Different Posts Per Page
   This plugin allows you to return different numbers of posts per page type.  For example, you can show five, ten or all your posts on your Archive, Category and Tag pages, but limit them to 1 or 3 or 5 on your home page.
5. WP-PageNavi
   This gives you an attractive way to scroll through your post-pages, and really aids navigation, especially on a large site.  See the bottom of the home page on the afore-mentioned art site for an example.
6. AZIndex
   This plugin will create a very flexible site index for you with the greatest of ease.  Very nice when organizing a large amount of content, and it auto-updates when new content is added.  This is such a well-written plugin, and has the best documentation of any plugin I have tried, which I really appreciate!
7. NextGEN Gallery
   I’m sure this makes it to everyone’s list.  I did not use it on this, my design site, but found it great for my art site.  I used it to include a random gallery of paintings on my sidebar, to include thumbnails of related images in posts, and to create indices of paintings and photos.  I could have used it for my art galleries of thumbnails and large images, but did not in this case, as I have my own art image database which contains a bit more information than the NextGen plugin displays.  The developers continue to improve this plugin; they have recently added the ability to include titles.
8. Yet Another PhotoBlog
   This is a very cool plugin that allows you to insert an image once, and it will create different sized thumbnails to be displayed on different types of pages; for example, you can display small thumbnails of an image in the archive pages, another size on the home page, and another size on the individual post pages, and you can specify left or right display in all cases.  It only allows for the insertion of one image per post, but you can use the standard WordPress image upload tool to add additional images.
9. TS Custom Widgets
   This plugin allows you to include different sidebar widgets on different pages.  I found it very useful in many cases; for example, it gave me the ability to remove redundencies, such as an About Me box on the About page, or a random painting gallery on the painting gallery page, and to limit certain items to appropriate pages only, such as a blog roll only on the links page.
10. Simple Tags
    This is a very flexible and powerful little plugin for managing your tags.  It allows you to mass edit your tags, show related posts, create content-sensitive tag cloud widgets, and more.
11. Contact Form 7
    This is very nearly everything it needs to be.  This plugin allows you to create multiple instances of contact forms, using the standard form elements, and includes the ability to add a simple Captcha.  The documentation could use a little help; so you may need to read through some of the responses on the plugin homepage and do some trial and error to figure out just how it works, but once you get through that, it works like a charm.  You may also want the Really Simple CAPTCHA plugin from the same developer — it used to be included, but now it’s a separate element — or the more robust WP-reCAPTCHA that I’ve used on this site.
12. Subscribe2
    A very simple plugin that allows your readers to easily subscribe to or unsubscribe from your blog.  It sends an email notification to the list of subscribers when new entries are posted.  You can also exclude notices from being sent on selected posts and pages.
13. Sociable
    This is about the fourth social network plugin I have tried that automatically add links on your posts to your favorite social bookmarking sites.  It is very flexible and unobtrusive.  I did love the look of one called “Sexy Bookmarks,” but it caused my pages not to validate.  I am using AddThis Social Bookmarking Widget on this site, and it’s great, too.  But Sociable may offer the most flexibility in what bookmarking sites you can include, and I like the faded icons that come to life when moused over.
14. Feed Reading Blogroll
    One of the things I loved on my Blogger blog was the Blog List that showed the latest updated blogs you are following, compete with newest post title and a thumbnail.  I loved seeing my artist blogger friends’ latest images displayed.  I searched and searched for something like that for WordPress, and this plugin is the closest thing I could find.  It works well, is pretty easy to set up, but lacks the thumbnail display.  Using Feed Reading Blogroll along with Interclue enabled on Firefox, I can still see the latest paintings from my artist blog list.
15. Broken Link Checker
    This checks your posts for broken links and missing images and notifies you on the dashboard if any are found.  Very handy for keeping link-rot out of your blog.
16. Maintenance Mode
    This plugin will add a splash page to your blog to lets visitors know your blog is down for maintenance.  Yet you can continue to work on and view your blog as a logged in administrator.
17. DashBar
    This plugin adds a tiny logo in the upper corner, if you are logged in, with a two-level drop down menu bar that appears on mouseover.  It allows easy access to the dashboard or to add, edit or manage new posts/pages/links, and more.  I find it very, very handy, though the logout does not seem to work for me.
18. Akismet
    For keeping out the spam in your comments.  It seems to work very well.
19. StatPress Reloaded
    Excellent and very detailed stats displayed right in your WordPress dashboard.    You can export them out, too.
20. Google Analyticator
    Easy to use plugin for adding your Google analytics code to your WordPress blog.  Works very well.

Related posts:

1. Texas Wax: New Artist Community Site Designed in WordPress
2. Redesigning my Decor Site for WordPress
3. Using Featured Images in WordPress Websites