There's an app I couldn't live without which is called "CloudApp." It's not known to most people, it's basically a small cloud icon in your status bar next to the clock. If you drag a file on top of it, it gets uploaded to their servers and as soon as it's done, copies right into your clipboard. The easiest and fastest way to share files with people, they also provide you with a shortened link of the file. There are also more uses to it, but that's the main one.
CloudApp
Likewise, another great app I use on a daily basis is BetterTouchTool. It allows me to configure custom trackpad gestures and assign them to whatever I want them to do for me (ie. triangle gesture plays or stops iTunes).
There are many more, I'll include a last one-- gfxCardStatus, very useful for any MacBook user as it allows you to switch between GPU or intel graphics in order to save battery power. You can also configure it to automatically switch to GPU when on battery, dynamic, intel, when not charging, etc.
These are all utility apps which I found on the dev's website, none of these did I download from the App Store, just to clarify. They are all free.
