Xara Xtreme is a vector graphics program that until recently was only available for Windows. There is now a version of Xara Xtreme for Linux that has been released under the GNU GPL. It's still only in version 0.7, but I've just downloaded it and installed in on Ubuntu Dapper and it works great.
Here is a screenshot of Xara Xtreme LX on Ubuntu 6.06:
The Linux version cannot do everything that the non-free Windows version can yet, but the feature list is growing.
I highly recommend downloading Xara Xtreme LX and giving it a try. It is a very sophisticated graphics editors as shown by these examples.