WordPress.com Cheat Sheet

Next Page

Break posts and pages into several ones by using:
<!--nextpage-->

Custom Read More

Customize your “Read more” text on posts using:
<!--more But wait, there’s more-->

Contact Form

Allow people to email you by adding this to your posts or pages using:
[contact-form]

Embed YouTube Video

You can embed these on posts or pages.
See: http://support.wordpress.com/videos/youtube/

Embed Google Maps

You can embed these on posts or pages.
See: http://support.wordpress.com/google-maps/

Display Source Code

See: http://en.support.wordpress.com/code/posting-source-code/

Allowed HTML Code

The following code is allowed within posts, pages, and widgets:
address, a, abbr, acronym, b, big, blockquote, br, caption, cite, class, code, col, del, dd, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, img, ins, kbd, li, p, pre, q, s, span, strike, strong, sub, sup, table, tbody, td, tfoot, tr, tt, ul, ol, var

More WordPress Shortcodes

For more of these, visit the official WordPress Support page.
See: http://support.wordpress.com/tag/shortcode/