Here are 5 of the best, in no particular order because the order depends on what you actually need to boost your SEO.

1. All-in-One SEO Pack

Take control of your meta descriptions and page titles. You can also tag posts with categories. All-in-One SEO Pack is one of the most popular SEO-related plugins because of the essential functions it allows you to perform.

2. Ultimate Tag Warrior

Another extremely popular plugin, Ultimate Tag Warrior helps you to add tags, which are recognized by search engines like Technorati, to each of your posts. UTW provides you with a few different options for entering tags, including simply typing your tags when you’re entering the post.

3. Related Entries

Internal linking is valuable for SEO and it can also help your readers to find additional content that may interest them. Related Entries will make the process easy. Your posts will automatically include links to related posts (in a list, at the bottom of the post).

4. SEO Title Tags

We’ve already mentioned title tags with the All-in-One SEO Pack, and SEO Title Tags provides another quality option. With this plugin you can easily control and optimize the titles of every page and post you create with WordPress.

5. Google Sitemap Generator

Google and other search engines use XML sitemaps to find and index all the pages of websites and blogs. By default your WordPress blog does not create an XML sitemap. With this plugin the process is automated. Additionally, it automatically updates the XML file whenever you publish a new post.