I've never solicited a sale (i.e. approached someone to sell them an image), but I have sold several images (some to very large national companies). In each case, the company has found me via my presence on the web (website, blog, Flickr, etc), so my advice would be to get as much exposure as possible.
As far as pricing goes, it depends on what the image is to be used for. I recently sold an image to a very large (for Canada) national transportation company, which was to be used in their internal newsletter for employees. For this, I gave them two options:
1. Pay $X for a single, one time use, in this publication only
2. Pay 1.2 times $X for use in perpetuity, in this publication only (this was the option they chose, not surprisingly)
The reason I stipulated "in this publication only" is that if they wanted to use the image in a national ad campaign, for instance, I would charge them more money because the image will have wider distribution. The actual dollar amount will vary depending on what the market can tolerate and the distribution size, but $200 is not out of the question for a moderately-sized company to use on a limited scale, in perpetuity.
You can stipulate any terms you like when selling an image; in the above example, I sold the rights to use the image in a particular publication, and that's it; in essence, a lifetime license. The image itself belongs to me, and I would never (ever) sell ownership of it; ownership of the image always belongs to the person who created it, unless they've specifically created it under contract for someone else. Basically, another company could purchase that same image and use it for their own purposes; I have not sold the rights to the image, just the right to use the image for a specific purpose.
Hope this helps.
I'm curious, because I have a shot which is absolutely superb for a company called Mad River Canoe. Of course, they would have to think so too.
