Every now and then I get asked about this, by both authors and commentors, so I’m listing a few good resources here so that they’re all together in one place.

For Blog Authors:

N.B. It’s worth noting that some of the short HTML tags (<i> <u> <s> etc) seem to be deprecated i.e. not all new browsers render them, so it’s often better to use the XHTML tags ( <em> <strong> etc) – except on platforms that don’t accept them, of course.

• Basic HTML for Bloggers.
  – from 2007, but excellent introduction
• Basic Blog HTML Language
  – introduction with a table listing TAG-ACTION-EXAMPLE for simple formatting
• Blogger HTML Tutorial
  – typically good introduction from eHow
• Basic HTML tag for bloggers
  – simple list of tags with formatting actions
• HTML Text Formatting
  – W3Schools is the best all-round resource, with widgets that allow you to test the code for yourself on their site – not much on detailed explanations though.

For Blog Commentors

In WordPress, the blog authors can use a wide range of HTML tags, while blog commentor’s options are restricted to some basic formatting tags. Other blogging systems similarly restrict the markup allowed in comments, in order to limit potential avenues for exploits.

• Html allowed in comments #2

Most of the articles listed above offer links to more advanced tutorials at the end of their own tute.