CSS-Tricks has a great responsive design. The Forums in particular are awesome. They look great at any resolution. There’s a little bit of text overlap on mobile but I’m DEFINITELY not complaining.
Then there are sites that are NOT responsive. Reddit in particular is notorious for not being responsive. But… check this out:
Notice anything? Reddit is functioning awesome! How? A little extension call Stylish. It allows you to set USER stylesheets for websites that you use often but may not have the best design. This is available on Chrome and Firefox.
Could be a great learning experience tweaking someone else’s design too! Enjoy.