mandar-marathe

Coders like to use spaces, carriage returns, new lines, tabs and indentation to make their HTML documents human-readable. This helps collaboration and debugging of the HTML document. However, all these features add to the filesize of the resultant HTML document. This structural information is totally ignored by browsers.
This plugin removes spaces, carriage returns, new lines and tabs from your HTML document. You can therefore freely use these features while writing HTML, safe in the knowledge that it will not bloat the final HTML document.
With this plugin you can also mark areas of your HTML template where you want to preserve white space – for example – in areas containing Javascript which needs carriage returns and new lines to function correctly.
HTML comments are not affected by this plugin.

WP-Compress-HTML

Reduces the HTML file size by removing unnecessary white space from the HTML document created by the WordPress blog.

LastLeaf

This plugin give writers an option to automatically add spaces before paragraphs. 
It’s mainly designed for Simplified Chinese users, because most of their paragraphs are indented by 4 spaces. 
In edit page, if paragraphs are not start with 4 spaces, the checkbox for auto adding spaces will show up. 
在文章编辑页，当有段落段首不以4个空格开头时，侧栏会出现“自动补足段首空格”的选项。
<h3>Arbitrary section</h3>

Add Indent Blanks

This plugin give writers an option to automatically add spaces before paragraphs.

WP-Compress-HTML vs Add Indent Blanks