A couple of useful sites for development

Unicode

Can be useful for looking up unicode code points. Particularly useful for looking up accented characters. Another interesting use is for UI graphics characters.

gist-hkan

This can be used to look-up emojis and shortcode for emojis.

color picker

Let you visually select a color so that you can paste its definition in your HTML or CSS documents

color names

This is a list of "standard" color names.