One of my must-have Mac OS X applications is TextExpander. It's a program that automatically expands abbreviations as you type. If you're familiar with the venerable TypeItForMe, or the way-back Thunder 7, then you get the concept.
If you don't t know those apps, well, here's a brief description. You can set up TextExpander so when you type "btw," the words "by the way" are automatically placed in your document instead. And this works for just about anything, including pictures. For example, you might type "mydogpict" and have it paste a photograph of your puppy into the current document.
TextExpander has some more advanced features, including the ability to integrate what's currently on your computer's clipboard, too. This is especially handy, once you get your mind around how it works. I use this feature to easily create links to Amazon products that include my affiliate identification. The publishers of TextExpander recently asked their customers for tips, so I wrote up how to accomplish this and it's now available on their blog, if you're interested in the details.