We already talked a lot about Pixelmator here on the site, because it really is one of the coolest Mac software today. This is a very complete graphic editor, but it is perfect for working with non-vector bitmap images. what comes in Affinity Designer, released a few weeks ago.
It is not developed by the same company as Pixelmator, but by Serif Labs.
Affinity Designer's own interface resembles that of Pixelmator, and it exploits several OS X technologies such as OpenGL, Grand Central Dispatch and Core Graphics, being fully optimized for use on Macs with multiple processors (already 64 bits, inclusive).
The software offers a work with visualization always at 60 frames per second, even using gradients, transformations, effects and adjustments in real time. It has support for PSD, PDF, SVG, AI (PDF Stream), Freehand and EPS files, advanced use of colors (CMYK, LAB, RGB and monochrome, with ICC management), complete editing of 16 bits per channel, slicing images, tablet integration and more.
Here's a little of what he's capable of:
Long live Affinity Designer (and Pixelmator)!
(tip from @iggorssoares)