Need a photography program for my Mac OS X with great edit options. Want to erase, cut paste?

I want to be able to cut something out, or erase it. Not crop it. The iPhoto blemish option is just not enough for the work I'm trying to do. But I don't want to pay a lot of money. I have tried Picasa on my Dell but its not much better. And I need it very user friendly. I know very little about this stuff!