Photoshop used to be the gold standard for photo editing. Today there are many free or darn cheap alternatives. Chip Chick does a great overview of some of the best choices out there. Of special note is Google’s Picasa. Google’s signature ethos shines through- it is super-easy to use and has most of the basic retouching items that you need. Also the help is abundant.
With such an easy available interface someone at Google needs to make some software to negotiate world peace.