The Adobe line of software (i.e. Photoshop and Lightroom) tend to be the standard for most. Exactly which editor you get really depends on the degree of editing you plan on doing. The good news is, you can download trials for free off the Adobe website. In short, Lightroom is designed primarily as a photo database, but also has quite powerful editing tools that can handle most basic touch-up, color correction, tone and contrast correction, along with many other basic editing needs quite nicely. Photoshop is a more dedicated editing tool with finer tuned and more powerful editing tools that can handle more dramatic photo editing (along with all the basics of course). Then, you have Photoshop Elements, which is a slimmed down (and significantly less expensive) version of Photoshop. There are certainly other programs out there, but I haven't used most of them personally.
Lastly, if you're looking to do very large prints, you may want to get specific software for "up-resing" your photos so they can be printed with acceptable quality at very large sizes (Photoshop can do it, but many photographers use dedicated software). I'm not sure exactly how big you want to print, though.
