Gimp is pretty good, and for a free software it has a lot to offer, check out the other free software in the sticky at the top of this forum section, some people don't like the interface but it doesn't seem too bad to me.
For a cheap-ish deal check out Photoshop elements (10 is the latest version) or a more fully featured software (but couriously not as popular) is Paint shop pro, Adobe Lightroom is another option. Another good but unpopular one is ACDCee pro