Hi, There are several SEO plugins for wordpress and you can find it by searching the word SEO in wordpress.org You might want to look at this link http://wordpress.org/extend/plugins/search.php?q=seo&sort= I personally have used "SEO Ultimate" and "SEO Tools" and both are good.
Here is a list of the top SEO plugins -- All-In-One-SEO, SEO Platinum, SEO Ultimate, and Yoast SEO (aka wordpress seo). I've used them all, and all are great; but Yoast is probably the best.
I have used all in one seo for a while now and its always worked well. It looks like they just changed it though so you have to donate to get all the benifits from it. Seems like a load of crap to me.
Personally I have tried a few but always go back to All-In-One-SEO. Another good SEO plugin you should install is SEO Friendly Images which will automatically adds alt and title attributes to all your images.