A sharebar is a widget that allows readers to share your blog to different social platforms such as Facebook, Twitter, Digg, StumbleUpon, Email and so on. Using this sharebar allows your readers to help you spread the word about your blog easily.
2) Popular Posts Widget
I really love this widget because it keeps my readers up to date on what's good at my blog. They will certainly be interested and can help promote your own posts to them.
3) Labels/Tag Cloud
These widgets help your readers get around easily in your blog. People can find what they want from these labels and just read the posts their interested about.
4) Your Blog Search
Allows readers to search relevant topics they want to know about in your blog.