this is what i use:

All in One SEO Pack or Yoast – allows you to optimize your SEO efforts for every single page on your site. Good SEO equals Good Traffic!

Auto Terms of Service and Privacy Policy -provides legal documents about your site and how you operate your site, essential for any serious webmaster.

Contact Form 7 – creates a professional contact form that your audience can use to contact you quickly and easily.

Cookies for Comments -a great plugin that filters out all of the spam from your site!

Sitemap Generator – gives you a good looking sitemap that Google will love and that your visitors can use.

Limit Login Attempts – prevents the number of people that can access your login page, an essential plugin to stop hackers.

Subscribe To Comments –this cool little plugin allows your visitors to easily stay in the discussion and keeps them informed on what others are saying on your site.

W3 Total Cache – makes your site as fast as it can be. This is very important for SEO because Google puts a lot of emphasis on site speed!

Social Sharing Toolkit –allows your audience to share and like your posts to their friends and family, important for SEO.

w3 total cache is the bees knees! I was using wp super cache before and it's no where near as powerful as w3. I prefer google xml sitemap over the other one recommended, but that's probably just personal preference. I also like Yoast bread crumbs, but it requires you to make a few changes to the core theme php. Additionally quick adsense is a decent adsense manager.

edit: exclude pages from navigation is good too if you don't want all of your pages in the navigation bar.

You will also do well to install some security plugins. I use BulletProof Security, Secure WordPress and OSE Firewall. However, don't overload your site with plugins as it will slow things down, if you don't need a plugin or are not making use of it, then deactivate it.

disclaimer, about page if you're into that kind of thing.

You should also have a backup procedure, in case something ever goes wrong with your site. You could use a plugin like backupwordpress to automate the process.