I like to use Picasa, Google's free photo editing software, to put finishing touches on my photos before I upload them. I use it to adjust color temperature, lighting, sharpen, etc. It's easy to use, and I get great results with it.
Google has just released a new version, Picasa 3. To see all the new features, and what has changed, CLICK HERE.
This is an image that I converted into black and white with Picasa.