Mostly command line stuff. You can also find these programs in the Ubuntu Software Center, but I find it more efficient to share them this way.
In the most recent release of Ubuntu, there is a shortcut for the command line! To bring it up, press:
Ctrl + Alt + T
Update & Upgrade
This is the first thing I run, every time. The first command refreshes the list of updated packages to download, and the second downloads them and installs them.
sudo apt-get update
sudo apt-get upgrade
With this program, I can search for and open programs and documents with a few keystrokes. Super + Spacebar, to be precise. This shortcut is customizable.
sudo apt-get install gnome-do
Ubuntu Restricted Extras
For me, this is essential. It installs flash, java, the mp3 codec, and more.
sudo apt-get install ubuntu-restricted-extras
It is handy to be able to run the occasional windows app.
sudo apt-get install wine