Codrops Playground
I’ve come across this only recently and I can tell you there is some pretty cool stuff in there. From effects to styles, from animations to interaction, the Codrops playground has got a lot of cool things.
http://tympanus.net/codrops/category/playground/
Font Awesome
Font Awesome is great, it’s an icon font built for Bootstrap. Lots of great, well designed icons are here and you can use it like a normal embedded font if you don’t use Bootstrap. As an honourable mention, if you can’t see an icon that you want you can check out Fontello. It’s pretty much the same thing, but it is an archive of a lot of great icon fonts, just like Font Awesome. You can simply pick and choose the fonts you want to use and then download them as an icon font. Great stuff. Continuing the mentions, there is also The Noun Project, a great resource for SVG graphics for use not only in web but in design in general.
Font Squirrel
This one is a no-brainer. Have a font that you want to use? Whack that bad boy in the generator on Font Squirrel and bam, web font. There is also an extensive library of fonts and web fonts too. You can also check out Google Web Fonts as well for a great archive of web fonts.
Stack Overflow
If Stack Overflow were a life coach or motivational speaker, we’d all be rich and living life to the fullest. If you have a development or coding issue, post it on Stack Overflow and the community will help you out. Or just try searching for your issue and the majority of the time someone is having the same or similar issue to you and there usually is a fix for said issue.
SASS
SASS is a great alternative to traditional CSS. It allows you to better organise your projects, reduce your stylesheet size, create variables that can allow you to alter one line of code to change several others, or saves you having to repeat the same code over and over, plus a bunch more cool features. There has even been some handy frameworks, such as Bourbon and Compass, that makes it even better.