Zoetrope

I didn't know there were tags to denote deleted text (I do now, use the <del></del> tag) or to denote recently inserted text using <ins></ins> tag.

Also, check out the presentation on The Elements of Meaningful XHTML if you never heard of other tags such as

• <thead></thead>
• <tbody></tbody> (denote heading and body of tables)
• <cite></cite> (citations)
• <label></label> (denote labels of form entries)
• <address></address> (contact info for a page)