Wordpress SEO: this is a most used plugins for Wordpress websites. With this user can specify basic things like page title, Meta description while creating a post.
Wordpress database backup: this plug-in emailed a backup of your site regularly so if any wrong things occur you can recover
your data.
Yet another related post Plugin (YARPP): with YARPP you can add multiple templates with thumbnails.
Akismet: with this Plugin you can avoid spam comments. You can activate it by entering an API key acquired from Akismet site.
Maintenance mode: if a website is modified or has some technical problem then having a splash page set up instead of an error page is a great support to customers. Maintenance mode will allow you to login in administrators to access the site.