Pixelmator, my photo and graphics weapon of choice, just got a really nice update. There are a lot of new features in this update.

There are shape tools and pallets, with dozens of built in shapes. (Watch the video)
There is an intriguing new "convert text into shape" feature, to apply apply gradients, shadows, strokes, or even reshape individual letters.
There is a new paint selection tool to speed up selections with a brush stroke. (Watch the video)
They've also added a light leak effect for retro-illuminated images. (Watch the video)

It's a free upgrade if you've already purchased the app. If not, I recommend getting a copy of Pixelmator. It is a really powerful photo tool for just $15.