The standard in digital photography editing, as most people know, is Adobe Photoshop. Photoshop's a really powerful program that can do everything from the simple basics, cropping, brightening, and sharpening your photos, to much, much more complex things like high end portrait editing, dropping out backgrounds, silhouetting images.
There's a whole lot of other programs out there as well, ones that Adobe makes and other companies, specifically Adobe Lightroom, which is a raw processing program similar to Photoshop. It's something you use before you bring a photo into Photoshop.
Similar to that is Adobe Bridge, which is an organizational viewing program that also works really closely with Photoshop but before the fact. If you want to go and experiment out there, there are a whole slew of other programs that you can use, however most people have accepted that Photoshop is the standard and pretty much the best editing program you can get.
Another nice thing about Adobe is, if you want to give a try, you can easily go to their website, download and get, I don't know, a 30 day free trial. The same goes for Lightroom and Bridge, and all their programs, so it' s really great.