Normally $15. (Which is still a good deal!)
By David Capello. (Who also participated in Speedhacks as recently as 2007.)
It's a nifty sprite art tool written with Allegro. I just got around to buying it with the Xmas sale. I played with it for a few minutes and I already like the feel of it. The buttons you need, with simple hotkeys, and everything else is out of the way. Just picking up pixels, and dropping them. I made a cute little wizard sprite by just starting with a blob and then thinking "what does this kind of look like?" and then just trimming it and shading it and boom. I'll post it when I get back up in the morning on my desktop PC.
It supports animations, onions, and a bunch of other stuff that programmer-me barely understands. But I definitely feel at home with it compared to 90's/DOS graphics tools I used to use for modding games / making my own sprites.
There's a free/trial version on his website, the second link if you want to try-before-you-buy.
Supports Windows, Mac OS X, and Linux!
Here's the version roadmap (currently 1.2, with crossed out pieces being done)
And I just realized he's open-sourced it on github with issue tracking/bug submissions:
Pixel art? Allegro? Open source? Linux and Mac OS X ports?