Here are some of the tools, services and websites that I highly recommend you to use or visit. I'll try to update this list so make sure you regularly check out this page for more cool stuff.
Graphicriver is an Envato marketplace. At GraphicRiver you can buy and sell royalty-free, layered Photoshop files, vectors, icon packs, Adobe add-ons and design templates for just a few dollars. It's a great place for designers to sell their designs. So be sure to sign up because it's free. Just make sure that you go through some of their marketplace documentation because there's a little multiple choice questions' test that you need to pass before you become eligible for selling your work.
If you're looking for some great inspirational stuff, then look no further, Niice is the way to go. Niice is basically a design search engine where it gets results from several big websites like Behance, Dribble, Fubiz and Designspiration. A little drawback to this website is that if you don't have a fast internet connection, you'll get irritated by the time it takes to load images. Other than that it's a great place for designers to get quality inspiration.
As the name implies, this website is used to convert any hex value to its RGB equivalent. This is a minimal and an extremely easy-to-use website. You should definitely try it.
If you're having trouble converting your pixel based layout to ems or vice versa, then Pixem is for you. Here you can either copy/paste your complete CSS or some specific lines from your CSS on this website and convert it in ems or pixels. Be sure to use this website in your next responsive layout project.
Specificity Calculator is a great way to visually understand Specificity. If you're unsure why some rule is overriding another, then this tool will help you easily understand that. We just need to paste the two conflicting CSS rules in their appropriate input boxes and it'll show us how much specificity our rules have. I would definitely recommend this website to all designers.
Balsamiq Mockups is a small graphical tool to sketch out user interfaces, for websites and web / desktop / mobile applications. Using this tool, you can make wireframes for your website and because it's digital, tweaking and rearranging different elements is quick and easy. They also provide free tutorials on their official website. Balsamiq also has a desktop version but unfortunately it's not free.
Launched in 2007, MindMeister is an online mind mapping software that allows its users to visualize their thinking (brainstorming). Brainstorming is the first step of creation. If you have a central idea, you need to properly structure your related thoughts in order to follow through with that idea. Based on the freemium model, MindMeister provides users three free fully featured maps, but charges a subscription fee for additional maps.
Bubbl is an online tool that enables users to create mind mapping and brainstorming diagrams online. To begin, the main topic/concept is entered in to the parent bubble. Then ideas and thoughts are recorded in colorful text bubbles linked to the parent bubble. Users continue to add text bubbles which are color coded according to hierarchy. The tool is Flash based, so you have to have Flash player installed in your browser. The great thing is that this tool is absolutely free but you should Sign Up first to export your mind maps into other formats.
The heading says it all, no need to elaborate. Just one more thing, THEY'RE ALL FREE!!!
It's a free jQuery plugin used to make step-by-step introduction or guide for your website.