What are your favourite free graphics programs? What tutorials are there for these free graphics programs that have really helped you in your developing?
Although I don't use very many free programs, even if I did I still know what my favorite would be: Blender!
It definitely has a steep learning curve; the trick for me was to experiment lots. It's best to start out by goofing off and exploring, instead of starting projects right away and hoping they will be usable. Or if you hate spending time on stuff you won't use, consider a poorly made model to be the equivalent of a "sketch" drawn on paper: not the final product, but a "rehearsal" to remind you of what your goal is and how you might (or might not!) go about making it.
Blender has changed so much over the past five years that most of the tutorials I relied on either no longer exist, or they wouldn't make any sense to people using newer versions of the program. Generally speaking, though, there are three kinds of resources that I would recommend:
1. I'd pick a video tutorial over a written one any day. Some processes (like modeling a soccer ball) are much easier shown than described, and if you're having trouble finding things on the program's interface, they can help immensely.
2. Blender 3D: Noob to Pro covers a ton of different concepts. I'm not sure how much it's kept up with the times, but out of all the written tutorials I've used, this series was some of the easiest to understand.
3. A good forum where you can ask for help, and see what tricks other people have learned. My favorite forum no longer exists, but there are plenty of others out there, including Blender.org's own official forum.