Whenever I start with a fresh operating system (which I do probably more than I strictly need to), there are certain tools that I just have to have. Here are a few of the most important desktop utilities.
Note: I use Xubuntu because I'm not geeky enough to run Debian, Ubuntu is destroying the universe with Unity, and I still love apt-get more than any other package manager. Also, XFCE is pretty great.
Kupfer is like Spotlight or SilverLight on the Mac, and various utilities on Linux and Windows. I practically never click an icon on my desktop or go to my window manager's menu bar, because I launch all my apps from Kupfer.
I'm always copying something, getting distracted, and pasting it later only to discover I've copied something else in the interim. Or wanting to have two or three copied items handy for some task.
This utility stores the last 10 (by default) items you've copied. You can click the icon in your toolbar to see previous items, and click an item to restore it to your current clipboard. I set my limit to 50, and this comes in handy for me many times every day.
There are many things I type many times per day. My e-mail address. The names of my company's products. Some common snippets of code.
With AutoKey, my life is a whole lot more fun. I type a few characters and they're automatically replaced with the whole command/sentence/paragraph/e-mail address I wanted.
In addition, you can save scripts written in Python, and give your automatic typing some dynamic qualities. Think sendkeys in Python.