Image Creating & Editing
Pixlr is a pretty popular web-based editor.
Sumopaint is another one that’s been around for a while. Pretty powerful, with premium features.
Photoshop has student plans, but is probably too pricey if you’re not a regular user.
The GIMP is a free Photoshop-type editor available for most operating systems. There are tutorials all over the web to help you get started.
On Windows, some people find Paint.net acceptable.
On the Mac, Pixelmator ($30) is a heavy Photoshop competitor.
We only talked briefly about vector graphics, but if your interested in messing around with them, the usual (expensive!) suspects are Adobe Illustrator and Corel Draw. A free Mac/Windows alternative is Inkscape.