I could come in here and list all the sites off the top of my head that have helped me in Web design, maybe look through my favorites and then on the favorites on the rest of the computers in our house but...
My site,
Free Webmaster Resources offers a much bigger "list" bigger than any favorites directory of mine and bigger than any number of sites I could think of off the top of my head. We also offer some content on our site like free templates and pro templates, but in general our site is just a giant favorites directory of helpful sites I have found useful as a webmaster.
Our site is likely to have some unique quality links as I started this Webmaser resource when I was barely a Webmaster and I had no idea what I was doing and was angry at the toughness on the internet to find quality sites with free content. I was using Dreamweaver and couldn't even code a table without it. Now as an advanced Webmaster there are additional links on our site that I find helpful now.
It's not specified whether mentioning your own site is advertising or not, but I'm hoping Mr. Tech won't remove this post as my site truly is very helpful as even I, the creator use it all the time.