I use stockcharts.com its not a software though, but I like it a lot for annotating, you should check it out. http://stockcharts.com/h-sc/ui btw: in prophet charts I can also add notes...
All new computers these days (the past few years) come with free image editing programs that also do annotation on images (chart is an image). In addition, most chart programs have their own annotation program although a little slow with less options as a stand alone image program that came with your computer. However, if you're looking for something more complex...try Snagit...it's free for 30 days. If you like it...buy it. I like it a lot because you can add some cool annotations on charts. http://www.snagit.com http://www.techsmith.com/download/snagittrial.asp
I decided to use FastStone Capture. It's not free but it has excellent, quick and easy to use annotation. http://www.faststone.org/ Thanks.