The Nike website is one of my favorite websites to use because it allows you to customize the design of a shoe that you want. The clean black text one white background is also very simple and elegent.
The Boosted board website is another one of my favorite websites that was designed really well with lots of gifs playing in the background with a very clean interface for users to browse.
Daesk is a time management app and their website is really cool. It is interactive and also very graphically appealing with bright colors and very little text.
Sketch.io is essentially a drawing app for your browser, it has very cool features and allows you to do pretty much anything a downloaded drawing app would.
Pixlr is like an online photoshop on a browser. It has many features that can be found in paid downloaded apps. Very easy to use and website is also very well designed.