There are too many plugins for wordpress which help you to improve your search engine optimization, but you can eventually download and install a couple of them and test which one work best for you, because in the blogsphere there are many plugins which do exactly the same.
Now I’m going to share with you a couple of plugins excellent for SEO, but also you can check the wordpress plugins data base for other plugins.
As you now the page titles are very powerful in the Search Engines, so this plugin really helps your WordPress blog’s optimization allowing you to give to each post its own unique title tag – one that is uncoupled from the title of the post. This enables you to write a title tag what is good for the Search Engines while keeping a post title that will appeal to humans. If you want to improve your SEO, you should start by downloading this plugin 
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This plugin is streamlined for some best practices for Wordpress SEO. While it gives you many options the defaults reflect the settings I recommend using. It have too many useful options as for example, add a description of the post for the meta tag, so when a potential reader find your post in a search engine it will see that description you wrote. Download this great plugin, I recommend it !.
Related Posts Plugin will generate a related posts list based on your tags, and also it add the related posts to your feed. You can set the mount of related posts you want to show plus another features like showing a comment counter.
This plugin creates a tag cloud for your blog by enabling you to group posts together based on “tags” you include when you write your posts. Tag clouds help your SEO by creating internal links to relevant pages using good keywords. Ultimate Tag Warrior is not compatible with WordPress 2.0 by itself, so be sure you download the Compatibility Thing. This plugin may be a bit difficult for non-coders to get working right.
This is a variety of “dofollow” plugin. It’s main function is to strip “nofollow” tags from links in comments. The purpose is to encourage comments by rewarding commenters with “dofollow” links which boosts their rank in search engine. However, this particular plugin also has features that thwart human’s who are paid to visit blogs and leave insipid comments simply to boost their companies back links.
I personally dislike this plugin, I don’t like to see all those many little icons at the bottom of my posts. Instead, I prefer to use the feedflares of feeburner, with them you can see a couple of links which I previous selected them.
If you use another plugin and you consider it’s very useful, please comment on this post to share it with all the community. In the following days I will be talking about search engine optimization on wordpress, stay closer 
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Hey! my name is Javier but you can call me Javo, everybody does.
Thanks for the post. I think I most of the ones you listed, but there are some (i.e. SEO Title Tag and All in One SEO Pack) that I need to install.
Jonathon’s last blog post..FriendFeed- Keep Track of How Your Friends and Family Interact on the Internet
Nice Jonathon, try them and then come back and tell us how useful they are.
I just installed them and now have them activated. I really like being able to remove the Blog Title association to each post.
Jonathon’s last blog post..FixMyMovie- Gives Your Mobile Phone, Digital Camera or Webcam Videos an Enhancement Makeover
I haven’t taken a close look at All In One SEO Pack yet, but I currently use the Add-Meta-Tags plugin, which appears to be very similar in nature.
As for the social bookmarks, have you checked out Add This (www.addthis.com) – It doesn’t take up a lot of space, but it gives your readers the ability to use their favorite social bookmarking site.
Zander Chance’s last blog post..Name The First CD You Ever Bought
Among those plugins I only use the 2nd & 3rd one, for me it should be enough for a blog
Edward’s last blog post..Sad life of an orange
Related Posts is a best plugin!
Social Bookmarking, i’ll try it.
Pretty good article. I like it, keep it up.
I think that was a pretty good post. I couldn’t do it
. Keep up the good work.
Thanks!
I’m using All in One SEO Pack, Related Posts, and Google XML Sitemaps for SEO purpose
Hosting Reviews last blog post..HostDime.com
I was using the Google XML Sitemap plugin but noticed a big drop in traffic… So, I pulled the plug
Traffic has been steadily increasing ever since.
Mikes last blog post..How To Sell To The Rich Part 2
Really Mike? thanks for the advice… I also experimented it too, but I didn’t pull the plug
, let’s see what happens now 
I don\’t normally leave comments, but your post really got me thinking! Thanks for this!
It’s a Nice for me! Thanks!
i personally prefer wordpress rather then anything coz they are so friendly. i found some good seo plugins there are really good and make ur work easier.