For all those front end web designers out there here are some great resources I have come across over time. I have one rule of thumb; If its useful and or has potential for at some point being useful to me (a front end web designer) then I will likely list it here. If something is missing, let me know!
HTML 5 Cheat Sheet
This cheat sheet is essentially a simple visual grid that contains a list of all HTML tags and of their related attributes supported by HTML 5. The simple visual style I used to design this sheet allows you to find at a glance everything you are looking for.
Web page test
Test a websites performance. Why? Because you are the worst judge of your site’s performance.
Responsive Web Design Testing Tool
Responsive Web Design Testing Tool. This tool has been built to help with testing your responsive websites while you design and build them.
JSFiddle - Share your Code
HTML Elements Index
A continuously updated list of all HTML and XHTML elements and their corresponding versions.
Web Standards Solutions
The Markup and Style Handbook. A definite must have for anyone learning web design. The book is easy to read through, insightful, and full of practical solutions for essential elements of web design.
Bulletproof Web Design ∴ Example Code
Example code from the master himself Dan Cederholm. The book is Bulletproof Web Design and I would say it's a must have for anyone learning web design.
Visibone Web Design Reference Sheets - What more can I say other than I loved this so much I bought it and use it on practically a daily basis. Sure this information is easily accessible on the web but it's a hell of a lot easier using this guys functional and equally beautiful layouts.
It allows you to download a World Wide Web site from the Internet to a local directory, building recursively all directories, getting HTML, images, and other files from the server to your computer.
Mock Up Tool
A rapid wireframing tool that looks and works great.