Websites:
https://www.smashingmagazine.com - Lots of good reading for design/front end.
http://tympanus.net/codrops - Excellent selection of cool demos. If you want to discover something to give your page that extra UI sparkle, this is the place to look.
https://css-tricks.com - Many informative articles on just about everything.
http://codepen.io - Not only is this a great way to quickly try out new techniques, but many people put up demos of small, handy code snippets. Browsing other people's pens and investigating how they were made is a quick way to discover new techniques.
https://github.com/sorrycc/awesome-javascript - Massive list of various javascript resources.
https://www.freecodecamp.com - Free fullstack Javascript Web Development Curriculum. Look on facebook and meetup.com for FCC meetups, too - the NYC branch holds them 3-4 times a week.
http://jstherightway.org - A curated list of best practices for virtually every topic in the JS language.
http://www.w3schools.com If you need a quick one sentence summary and basic example of something, go here. Look at the subtopics and you'll learn the vocabulary of a given task very quickly. (Note: older programmers will often remember this site being terrible and advise you to avoid it, but it's improved a lot in recent years and is now a great quick resource.)
https://developer.mozilla.org - If you need an in depth, 10 paragraph of something, go here. A little dry, but very complete.
https://unsplash.com Free high-res images, all in the public domain. Great for splash pages--example usage here.
Books:
CSS Secrets: Better Solutions to Everyday Web Design Problems - Intermediate to Expert CSS.
Eloquent Javascript - Great general overview of the Javascript language. Free.
You Don't Know JS - Goes into more depth on specific Javascript microtopics. Free.
Inspiration:
http://damian.drygiel.com/ - Lots of cool interactive stuff here. And slanty divs!
https://acko.net/blog/how-to-fold-a-julia-fractal/ - Mathematics visualization like you've never seen before.
http://threejs.org/examples/css3d_periodictable.html - Iron Man 2, coming to a browser near you. You can scroll, zoom, rotate and more.