Basic Tags
<html></html> Creates an HTML document
<head></head> Sets off the title and other information that isn't displayed on the web page itself
<body></body> Sets off the visible portion of the document
Meta and other unseen markup
<!DOCTYPE> Declares the doctype so the browser knows whether to expect HTML4 (<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">) or HTML5 (<!DOCTYPE html>)
<meta /> Metadata tag, typically used to telling the browser how to behave at different sizes and for search engines/social networks to pull headline, photo and description when shared
<link /> Link tags are used to attach external documents to your HTML. Most commonly used to attach CSS stylesheets and RSS feeds
<script></script> Script tags are used to attach Javascript files to your HTML, or author JS right on the page.
<!-- COMMENT TEXT --> Inserting comments in your HTML can be useful for leaving yourself notes in case you need to revisit your code later
Text Tags
<pre></pre> Creates preformatted text
<h1></h1> Creates the largest headline
<h6></h6> Creates the smallest headline
<strong></strong> Creates bold text
<em></em> Creates italic text (em for emphasize)
Links
<a href="URL"></a> Creates a hyperlink
<a href="mailto:EMAIL"></a> Creates a mailto link
<a href="#ID"></a> Creates an anchor tag -- a link to a location within this document
Formatting
<p></p> Creates a new paragraph
<br /> Inserts a line break
<ol></ol> Creates a numbered list (ol stands for ordered list)
<ul></ul> Creates a bulleted list (ul stands for unordered list)
<li></li> Precedes each list item, and adds a number or symbol depending upon the type of list selected
<div></div> A generic tag used to format large blocks of HTML, also used for stylesheets
<img src="url" /> Adds an image
<hr /> Inserts a horizontal rule
Tables -- CAN NOT BE MADE TRULY RESPONSIVE
<table></table> Creates a table
<tr></tr> Creates a row
<td></td> Creates a cell
<th></th> Creates a header cell (top of the column)