It's funny but I tend to use several applications to create and manipulate images. This is useful when your application needs some icon or image. Thus I would create a simple version of the image and add it to my code. I also send out a request to get a more appropriate image but this way, these requests can be collected and given as a task to a third-party graphic designer as a bunch of orders. And in the meantime, the application still looks good in design-time and the image requirements are also clearly defined before the external artists gets to do his job.
For an internal project I even used a render-engine to create a few images of a pretty CGI-girl holding signs, pointing at things and just looking at the user expecting they would replaced sooner or later. As it turns out, management liked those images, so they're going to stay! :-)
So, most important tool for developers: something to work with graphics. (Paint Shop Pro for image manipulation, Poser Pro from SmithMicro to render pretty women.)