Here's a collection of best and most useful blog widgets or add-ons that can be easily integrated with any website/blog. All these below add-ons are 100% Free and they are very easy to install.
Outbrain Star Ratings Widget: Very eager to know what your readers think about your posts?
Here is a cool star rating widget by Outbrain. The insttallation is very simple,
just follow the step by step instructions on their site.
ShareThis or AddThis : Sharethis or Addthis social bookmarking buttons makes it easy for your visitors to share your content with others. It is a good way to increase your link popularity and publicity. Their nice css dropdown icons reduces the clutter on your pages and eliminates the need to add a different button for each social bookmarking service.
whos.amung.us : This is a real time visitor tracking widget and displays the number of people currently on your site and what pages they are reading. You don't need any sign-up's to grab this widget.ZOHO Creator: With Zoho Creator, you can create professional online contact forms/web forums in minutes. The good things about this is there are no data limits and readers can also upload attachments while submitting the form.
Google Talk Badge: Google Talk Badge will let your visitors to chat with you.The badge will active whenever you sign in to Googletalk. The nice thing is your visitors can chat with you even if they don't have a google account.
Yahoo Media Player: With this very useful widget, you can easily add a simple media player to your blog which can auto detect mp3 links and create an embedded player. This tool is very useful for especially audio,music blogs.
Cbox: Cbox or Chatbox is a chat widget which can be easily embedded
in any web page. It is free and have many features including message
history, spam blocking,etc. It can be easily customizable to fit your
Google Translate: This widget lets your non-English speaking
visitors to quickly translate your webpage in their native
language with just a single click.