I use Adobe photoshop light room 2 pretty good but it does more than what the average user would probably use. It's worth about $350-400 at Future shop well worth it but time consuming so you only use it on quality shots....But if you were to snoop around the net....lets say at some file sharing torrent sites...you can find it for free....just you can't update it...But you should really buy it from a reputable place .....Myself I will upgrading to Adobe CS5 when I find a version for mac ...cheap
You can usually download a trial versions to try out or go to youtube and watch tutorials....well cause I'm to lazy to read manuals
I use Photoshop CS5 and Adobe Lightroom 3.0 for my photos. I Do most everything in Lightroom and then export to Photoshop those that deserve an extra artsy touch. Both are expensive and not always user friendly.
You can get a cheaper version of Photoshop called Photoshop Elements and it will do most of what you want. It's about $100.
I also like Corel and Corel Paint and they are both affordable, versatile, and pretty easy to use.