Here are five of the best Linux graphics applications. I've linked to the sites of each of these applications, but check your distro's software manager first to download and install them.
LibreOffice Draw is part of the LibreOffice suite of applications. It's well suited for diagrams, charts, sketches and other graphics needs. Draw can also import graphics in various formats, and you can export your work to flash format if you want.
Draw offers a lot of features and functionality, and the nice thing about it is that you also get the rest of the office suite along with it.
Scribus provides professional page layout software to Linux users. You can use to create publications that rival costly publishing software. Scribus produces RIP-ready PDF files. The Scribus site has some useful tutorials and how-tos that will get you started using the software. Soon you'll be producing your own professional looking publications with Scribus.
Inscape is an advanced open source vector graphics editor. It's similar to CorelDraw or Illustrator. Instkape supports markers, clones, alpha blending and other advanced SVG features.
You'll find helpful tutorials and articles on the Inkscape site that will get you started if you haven't used it before. You can also ask questions via mailing lists and forums.
GIMP is short for GNU Image Manipulation Program. It's nearly on par with Photoshop and works very well for any sort of image manipulation. GIMP lets you enhance photos and do digital retouching in a wide variety of formats including TIFF, JPEG, GIF, PNG and PSD.
The GIMP site features tutorials, documentation and an introduction page to get you started using GIMP for your image editing.
Blender is a terrific tool for 3D work. It's on par with costly 3D graphics applications. You can do an enormous amount of things related to interface, modeling, rigging, rendering, animation, shading, UV unwrapping, imaging and compositing, physics and particles, and files.
To see a full list of features, check out the features page on the Blender site.
What's your take on this list? Are there other programs you prefer? Share your thoughts in the comments below.