What are some good editing apps for an apple computer?

I have a macbook air and I'm really into taking pictures on my nikon camera. I love editing but it seem like I can never find the right app. I'm willing to pay below 30$, I know the my computer has an app store, and I don't use it much, but I would like to start!

IPhoto which comes on your Mac is wonderful for photo editing.

Also check out Picasa 3 which is absolutely outstanding for editing, and it's free!

Picasa: http://picasa.google.com/

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