Free: Contests & Raffles.
I think Photoshop and Lightroom are the standard. They also cost but is easy to get help for them.One I have used recently is Photoscape it is free and intuitive. Cheap way to get your feet wet anyway.
Which version?
I currently just use iPhoto - the free program that came with my iMac.I plan to buy the newest version of Photoshop Elements soon - elements 8 I think it's called. I don't plan to do anything with my photos that would require more than what a basic program like Elements can do. Wildlife and nature images are supposed to look natural, aren't they? So I think that all of the surreal effects, layering, etc. that can be achieved with CS4 are really unnecessary for those who shoot natural images and want to keep them looking natural and realistic.