For SEO Purpose I'm using a few wordpress plugins which are doing a good job for me.
1- All in One SEO Pack
This is a must have plugin for SEO purposes and works out of the box. No configuration is needed. You just have to fill in the title, description and the keywords of each post before publishing.
(I have also used Headspace2 which is also a very good alternative to All in One SEO Pack)

2- SEO Friendly Images
This plugin automatically adds alt and title tags to the images of the site which help in better SEO position in google images.

3- SEO Smart Links
SEO Smart Links provides automatic SEO benefits for your site in addition to custom keyword lists, nofollow and much more

4- SEO No Duplicate
This plugin helps you manage your search engine duplicate content, by setting your post page’s canonical to the permalink.

5- SEO Booster Lite
This is the latest plugin I'm testing and like the idea behind it. It attempts to boost our search rank in google for certain keywords especially for which our site results are coming on the second search page. I have benefited from it a little till now. Still testing.