Inkscape is a freeware open source vector graphics editor, similar to Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format.
This application supports many advanced SVG features such as markers, clones, alpha blending, etc. It is very easy to edit nodes, perform complex path operations, trace bitmaps, import/export EPS, PDF, DXF files or export to HPGL, PNG, OCAL, JavaFX etc. It support's timed autosave in order to prevent your work. There is also a built-in spell checker which checks all visible text objects in your document by pressing "Ctrl+Alt+K" buttons.
More information about Inkscape can be found here.
For portable installation downolad "InkscapePortable_0.47.paf.exe", extract Inkscape in a folder of your choice and double click "InkscapePortable.exe".
Enjoy!