Guardfather's top free software and services picks.
Ubuntu has a great feature called the Ubuntu Software Center. Unless otherwise stated, any software listed here should be available in the current version of Ubuntu's Software Center, with a full description. I will still include links to the web pages for each program for convenience.
GIMP is the go-to image editing program for Ubuntu, and is available in the software center. If you've used GIMP in Windows, you should already be used to it.
Inkscape is a scalable vector graphics image editor. The interface is intuitive and easy for even inexperienced users to experiment with.
Audacity is a cross-platform sound editor which supports Ogg Vorbis, MP2, MP3, WAV, AIFF, and AU formats. It can be installed from the Software Center.
Pitivi handles multiple video formats, and is in active development. It features a powerful and intuitive interface which both experienced and inexperienced users should find easy to use, with minimal research.
This is the only screen capture software I had success with in Ubuntu. It makes it easy to record video from either your entire screen, or just a portion of it.