Since before OS X we've been using Stickies to hold small pieces of important information that we need at hand.
There is a really powerful small feature of the Stickies.app in OS X that let's any sticky note float over all other windows making it visible at all times. To make a sticky float above all windows select it and press: Apple-Alt-F (Command-Option-F)
This is really useful when you have to consider and copy info from several sources for the job you're working on. Remember you can have all kinds of info on your Stickies, not just text.