Pixen is a great graphics application for making pixel and small-scale art on the Mac.
Pixen is the best program for the pixel artist using
Mac OS X
. There is no competition, not even from the huge companies with several-hundred-dollar software suites. Their applications are inferior for pixel art, by virtue of their being conceived with a completely different intent. Pixen is specifically for small-scale or pixel art; it shines better there than any other application. Not only that, but Pixen carries no price tag: it's open source under the MIT license and absolutely free.
They make a bold claim, that's for sure, but after some time playing with it, I'm not sure if they're right on the money. I'm not really a "pixel-artist" but I've had to bust out a few icons in my day, and I wish I had a tool as suited to pixel work as Pixen.
Pixen is a free beta download for Mac OS X 10.3 +.