SVG tools

Official Resources:
http://www.svgi.org/
An almost comprehensive list of vector drawing programs(actually some 3d software is included as well):
http://www.maa.org/editorial/mathgames/mathgames_08_01_05.html

Free Editors:
Inkscape(most popular open source one): Besides svg, it can save file as .ps, .eps ... It also allows users to export file to .PNG(just .png, not .jpeg or .gif).
yED: a good graph editor which can automatically beautify line layout in the graph.

Standalone Viewer:
Batik Squiggle(pure Java): zoom in/out, transform... Can export .svg to .png, .jpeg and .gif.

Convertor :
ImageMagick: a powerful command line tool which provides functionalities of conversion, edition and composition. .svg can be converted to .jpg, .gif, .eps, ...

Conversion of .svg to .eps: Inkscape provides a better result than ImageMagick.

Useful free graphic software

Some useful image processing software:
Of course, Photoshop is a good one but it is not free. Some free ones exist out there. Here is a list which introduces some excellent free image processing software. GIMP, Paint.NET, Photobie, PhotoFiltre. This site contains more software.

With popularity of web 2.0 apps, many online image processing apps emerge. I list some ones I know:
http://fotoflexer.com/
http://www.picnik.com/
https://www.photoshop.com/express/landing.html
http://www.cellsea.com/media/index.htm
http://www.creatingonline.com/Online_Image_Editor/index.html
http://www.phixr.com/photo/userindex
http://www.lunapic.com/editor/
http://www.picresize.com/

Online Image resizer/optimizer:
http://webresizer.com/
http://www.resize2mail.com/
http://www.shrinkpictures.com/
http://www.resizr.com/
http://resizr.lord-lance.com/ (only .gif is accepted)
http://www.resizeimage.4u2ges.com/
http://www.picresize.com/
http://online-image-resize.kategorie.cz/
http://rsizr.com/
http://rsizr.com/ (Crop and resize)
http://www.freeimageconverter.com/
Standalone software:
http://www.imageresizer.com/
http://bluefive.pair.com/pixresizer.htm
http://www.imageconverterplus.com/ (seems a good one, but not free)
http://adionsoft.net/fastimageresize/
http://www.microsoft.com/windowsxp/downloads/powertoys/xppowertoys.mspx (MS image resizer power toy)

Vector Graphic Tools:
Inkscape, Dia, Synfig(Animation software), yED(good line layout), Sodipodi(not under active development, continue on Inkscape), Xara Xtreme for Linux, Zcubes(online vector drawing tool), Skencil(only on Unix/Linux)
Sketsa(SVG editor, not free)

Free desktop publish tool:
Scribus

Image viewer:
irfanview, xnview