PXL8 is a new pixel art software currently in development and finally ready for beta testing. It's designed to work with limited palettes at low resolutions, with a minimalistic interface.
PXL8 works on windows, linux, and mac and is set for a full release later this year. Beta testers get the program for free after the beta ends.
If you want to know more, head over to the beta signup page at http://www.nose-dive.com/beta/ . There's a timelapse video of the program in action. If you're interested in testing, fill in the form on the bottom of the page. Pixel artists of all skill levels are welcome!