I meant to do this post about two weeks ago, but it's better late than never. There are tons of these types of posts out there, but oh well.
Here are my list of plugins that I use on this site and nearly all sites that I (or my virtual assistants) create:
Akismet - No brainer. It's by far the best spam protection that you can get for your blog. Without it, having a blog gets really annoying - really fast.
All-in-one SEO Pack - Essential for out-of-the-box SEO for WordPress. I've been using this plugin for years and it works great. However, knowing how to configure it can be a little intimidating. Luckily, here is a really good video (albeit outdated) that gives a great tutorial on SEO and how to configure the plugin: http://www.craigfifield.com/all-in-one-seo.htm
Blubrry Powerpress - A great plugin for podcasting. Plays really nice with iTunes and has a built-in statistics system that you can configure.
Broken Link Checker - As you start blogging, you'll start to see that some of the resources you link to start to die off. This little plugin helps you to find them without spending hours scouring through your posts. If it find a dead link, it'll cross it out. Pretty cool sweet.
cbnet Ping Optimizer - By default WordPress pings sites on your ping list whenever you update a post. This stops that so you don't get branded as a ping spammer. Not sure how valuable it is since I've never been marked as a ping spammer without it.
Digg Digg - a social media sharer that let's you put social media icons in your post or float them off to the side. A little bit buggy sometimes, but I like it.
Contact form 7 - The most popular and best supported WordPress form. Not too intuitive to use at first. However, when you get used to the shortcodes that it uses, it's pretty awesome to see what you can do with it.
Google XML Sitemaps - Automatically creates an XML sitemap for Google and other search engines. In essence, it's an easy way to tell Google that you've updated your site and give them a link structure. Google likes that and will reward you with faster indexing and better ranking.
Insights - Adds a search area underneath the post editor that allows you to easily find and link to posts, Wikipedia, Google, etc. Helps a great deal with internal linking within the body of your post.
IntenseDebate - A commenting plugin. The reason why I like it so much is because, when users post a comment with the normal WP commenting system, the only way they'll know that you replied is if they come back to the same post. But with IntenseDebate, when you reply it send an email to the users. This means that they are more likely to respond and keep the conversation going.
Mailchimp - Aside from being an awesome and free email newsletter service, Mailchimp has a pretty cool widget program that you can customize for email newsletter sign up.
Maintenance Mode - Let's me work on my site without letting everyone see what I am doing.
Maxblogpress Affiliate Ninja - Let's you cloak your affiliate links and make them look prettier. I really like the plugin, but I highly suggest that if you are going to use it, create a disclaimer page that let's your readers know that you get money from some of the links that you recommend. It's just good and honest business.
Meet Your Commentors - Whenever someone comments on your site, it shows you all of their social network profiles on the WP dashboard. Great to build relationships.
No Self Pings - I hate when you link to another post on your blog and you get a pingback for it. This stops that.
Quick Cache - A lightweight caching plugin that protects you from server crashes when you get too many visitors.
Scribe SEO - This little plugin analyzes my blog posts to make sure that I am writing them correctly for the seach engines. Typically, I use this to train my virtual assistants on how to do On-Page SEO. I just tell them the keywords I want them to target, and that their post should be 100% SEO ready.
SEO Smart Links - Let's you create keywords that will automatically link to internal and external posts. Great for when you have a podcast and have your virtual assistants creating transcripts. That way they don't have to waste time finding and inserting links.
Subscribe Sidebar - creates a list of ways people can subscribe to your podcast or blog RSS feed.
Tweet Old Post - I LOVE this plugin. It lets you automatically promote your old posts on Twitter. You can configure it to tweet in various intervals, and how old posts need to be that you want tweeted. It's a great way to get re-tweets.
WordPress.com Stats - Just another stats plugin. I like it because it's instantaneous, unlike Google Analytics.
WordPress Database Backups - Backs up your posts and comments. Best part about it is that you can schedule your backups. However, it does not backup your theme.
Yet Another Related Posts Plugin - Great way to introduce readers to similar posts. Plus, it helps with your internal linking.
That's it! I'll add more to this posts I find more valuable plugins, or reasons why I've deleted some. Let me know if what plugins you think work well in the comments!