1. All In One SEO Pack – A Must have Plugin for your blog. Its an easy to use plugin and gives you power to optimize your further with catchy titles and meta description. Another thing it saves your from violating Google's Duplicate Content Penalty as it allows you to use unique titles on each post.
2. Comment Luv – Comments are life line of your blog and you want your visitors to comment. Most will only comment if they get something in return. Comment Luv enables you to show some love in return straight away by including a titled link to their last blog post or tweet at the end of their comment.
3. TweetMeMe – You sure must have seen this plugin on many popular blog. Your blog can go viral with this easy to use plugin.
4. Yet Another Related Posts Plugin – YARPP as its known as in bloggin world, provides a list of posts and/or pages related or similar to the current post/page introducing the reader to other relevant content on your site. It simply groups similar related posts and helps your click through rates.
5. Sexy Bookmarks - As name suggests its sexiest sharing plugin out there. There are many similar plugins but this is the best in terms of looks. So Go for it!