<!--...--> Defines a comment
<!DOCTYPE> Defines the document type
<a> Defines a hyperlink
<abbr> Defines an abbreviation
<acronym> Not supported in HTML5. Defines an acronym
<address> Defines contact information for the author/owner of a document
<applet> Not supported in HTML5. Deprecated in HTML 4.01. Defines an embedded applet
<area> Defines an area inside an image-map
<article> Defines an article
<aside> Defines content aside from the page content
<audio> Defines sound content
<b> Defines bold text
<base> Specifies the base URL/target for all relative URLs in a document
<base> Specifies the base URL/target for all relative URLs in a document
<basefont> Not supported in HTML5. Deprecated in HTML 4.01. Specifies a default color, size, and font for all text in a document
<bdi>New Isolates a part of text that might be formatted in a different direction from other text outside it
<bdo> Overrides the current text direction
<big> Not supported in HTML5. Defines big text
<blockquote> Defines a section that is quoted from another source
<body> Defines the document's body
<br> Defines a single line break
<button> Defines a clickable button
<canvas> Used to draw graphics, on the fly, via scripting (usually JavaScript)
<caption> Defines a table caption
<center> Not supported in HTML5. Deprecated in HTML 4.01. Defines centered text
<cite> Defines the title of a work
<code> Defines a piece of computer code
<col> Specifies column properties for each column within a <colgroup> element
<colgroup> Specifies a group of one or more columns in a table for formatting
<command> Defines a command button that a user can invoke
<datalist> Specifies a list of pre-defined options for input controls
<dd> Defines a description of an item in a definition list
<del> Defines text that has been deleted from a document
<details> Defines additional details that the user can view or hide
<dfn> Defines a definition term
<dialog> Defines a dialog box or window
<dir> Not supported in HTML5. Deprecated in HTML 4.01. Defines a directory list
<div> Defines a section in a document
<dl> Defines a definition list
<dt> Defines a term (an item) in a definition list
<em> Defines emphasized text
<embed> Defines a container for an external (non-HTML) application
<fieldset> Groups related elements in a form
<figcaption> Defines a caption for a <figure> element
<figure> Specifies self-contained content
<font> Not supported in HTML5. Deprecated in HTML 4.01. Defines font, color, and size for text
<footer> Defines a footer for a document or section
<form> Defines an HTML form for user input
<frame> Not supported in HTML5. Defines a window (a frame) in a frameset
<frameset> Not supported in HTML5. Defines a set of frames
<h1> to <h6> Defines HTML headings
<head> Defines information about the document
<header> Defines a header for a document or section
<hgroup> Groups heading (<h1> to <h6>) elements
<hr> Defines a thematic change in the content
<html> Defines the root of an HTML document
<i> Defines a part of text in an alternate voice or mood
<iframe> Defines an inline frame
<img> Defines an image
<input> Defines an input control
<ins> Defines a text that has been inserted into a document
<kbd> Defines keyboard input
<keygen> Defines a key-pair generator field (for forms)
<label> Defines a label for an <input> element
<legend> Defines a caption for a <fieldset>, < figure>, or <details> element
<li> Defines a list item
<link> Defines the relationship between a document and an external resource (most used to link to style sheets)
<map> Defines a client-side image-map
<mark>New Defines marked/highlighted text
<menu> Defines a list /menu of commands
<meta> Defines metadata about an HTML document
<meter>New Defines a scalar measurement within a known range (a gauge)
<nav>New Defines navigation links
<noframes> Not supported in HTML5. Defines an alternate content for users that do not support frames
<noscript> Defines an alternate content for users that do not support client-side scripts
<object> Defines an embedded object
I'll add more soon
