WordPress – How to Create a Timeline on Blog

From Google Docs Help:

Publishing

Once you're done creating and editing your spreadsheet, you can publish it to a webpage. >Just click the Share drop-down menu on the top right and choose Publish as a webpage. Then, click Publish now.

Then, everyone you choose can access your spreadsheet by entering the URL you send them into their browser's address bar.

Even after you publish a spreadsheet, it won't appear in any search index.

Embedding

After you publish your spreadsheet, you can share it with the world by embedding it (or parts of it) in a website or blog.

Publish your spreadsheet following the steps listed above and a unique URL is generated. Use this URL to embed the spreadsheet on your website or blog. You can also insert a spreadsheet in Google Sites. Just click Edit page > Insert > Spreadsheet from within your site. You'll need to enter the URL of your spreadsheet to embed it.

You cannot install any custom plugins on Wordpress.com for related posts. Unfortunately.

The one I've used and abused is called Yet Another Related Posts Plugin. It's highly customizable, free, and has the widget that you want.

As of June 2012, there is no feature built-in to Wordpress.com to display related posts.