I do a lot of web development. So here is some stuff I came around.
CSS and disabled JavaScript
Web design for browsers that have javascript disabled - but css enabled but still work.
Form Layout with CSS
Alligning Forms with css is always a pain. Especially when you touch the mobile world. But there exist a not-so-commonly known way how to make it a little easier to handle.
Working with Data: JSON and Forms
When creating applications on the web (I am not talking about simple consumer web-pages!) many frameworks try to merge UI (HTML) and Data (Java)... but to be honest: you do not need a huge framework (like GWT) for that.