I chose Picasa because you are a beginner, and Picasa is free. I also have Lightroom and Photoshop Elements 10. However, most of my quick fixes are with Picasa so I can share with friends and family for a few via email, and larger groups via Picasa web albums. It's easy, and Picasa editor is more helpful than it was a few years ago. To "fix" your photo took about 15 seconds.
If you plan to purchase editing software, I would recommend Photoshop Elements latest edition - #11. Others will suggest Lightroom and/or the full version of Photoshop. There are some learning curves to all the software, but Picasa is the lowest, and Elements would be next, in my estimation. Don't be afraid to also play with the Canon supplied software, especially when processing RAW files. You should start learning about it using the free Canon tutorials.