This plugin is my go-to SEO Optimization tool for WordPress. Other than the built-in "permalink" service, this is really a must have for your website to fare well in Google (and other) search rankings. With the All In One SEO Pack, they enable you to format the titles on every single page, which I see as the most important feature for getting ranked well in searches. Notice how each page on theNetFool.com displays "Article Info | The Net Fool"? You can format your blog like this with All In One!
This plugin goes far beyond merely changing around titles however, you can pretty much change around anything with the meta descriptions of your postings, your selected keywords that show up in search results, and even the ability to "nofollow" posts/pages of your choosing. In order to get your website search engine optimized, you need a tool like All In One SEO... and this one's absolutely FREE :D
2. OIO Publisher
I recently discovered this amazing WordPress plugin that "ads" a whole new functionality to your WordPress blog. Of course, I am talking about OIO Publisher, which allows you to run your own ad service where people can purchase ad slots on your page, pay through PayPal, and see their ads appear automatically! This one will run you a $37 one-time fee, but it is well worth it. It's been called the "ultimate sales platform" for your blog, and it is a lot cheaper than the alternatives which can cost over $100.
Gone are the days when you need to pay other services a percentage of your sales for allowing them to run your ad service. OIO Publisher is a winner in my eyes. The user interface is very easy to understand, and they have an entire marketplace set up that you gain access to once you pay for the plugin. This will allow you to run everything from inline ads and banner ads, to sponsored posts and text links. If you have a digital item to sell, you can use OIO to handle the processing as well. If you are serious about monetizing your blog, buy this plugin.
There is a reason that this spam-assassin comes with every WordPress installation. Before I was using Akismet, I had by comment moderation setting so that I needed to approve everything that came my way. Gone are the days where this is needed. Akismet is free to use so long as you aren't a major company, and is basically an entire spam network that builds on itself. Whenever spam is recognized on your comments, it is added to the Akismet database and will never bother you again. It has caught over 150 messages since I have started using it, and is a must-have for any serious blogger.
I had the unfortunate experience of being labeled as spam in the past. This definitely does not happen to more than 5% of commenters, but as soon as I sent an email to the moderators at Akismet, they cleared it up for me and I haven't had any problems since :). With this installed, you really don't have to worry about your comments being out of line again!
4. Related Posts
There are several "related post" plugins available for free through WordPress. In my opinion, the best of which is akismet alternatives WASABI Related Entries plugin. This is really a must-have option for your blogs. Not only does it look great and encourage your readers to stay on your website, but it acts as a great SEO tool by linking together your website for easier indexing! Again, there are tons of clones claiming to be the original and the best. I don't really know enough to say which was the first, but I think the WASABI-version is the most functional so I encourage you to check it out first!