So since I can't see a thread already I thought I'd post some links to my favorite opensource applications related to graphics.
I'm a big fan of opensource(http://en.wikipedia.org/wiki/Opensource) software particularly when it comes to my hobbies and interests as its obviously free, safe and usually well supported with documents etc.
Windows + linux, image manipulation software, tablet friendly. Not quite photoshop but works well.
Comprehensive 3d modeling and rendering.
Color Scheme Designer 3
If your color theory is a bit pants and you want to dabble with some colors then this is the webpage for you. It can simulate various medical conditions to see what your colors will look like.
You can export your colors in various formats (photoshop or plain html)
Record your screen + webcam + audio to a movie or SWF for playback on the web. The Flash export works really well. You can change various settings such as auto pan, annotations and playback speed (timelapse) etc.
Ideal for all you experts wanting to do tutorials hint
Not opensource, but a free one exists and the full version costs peanuts.
<loads> you can always pm me or reply to this list, I'm happy to point you in the direction of something as long as its free/opensource.