I made the above drawing of my daughters while we were hanging out at the playground next to their school. I created it in Edge Touch on my iPhone and I'm really impressed with this app. I've tried a few other pixel art apps but this one had all the features I could hope for: an HLS slider to fine tune colors, customizable color palettes, and GIF export. Add to that layers, animation and even onion skinning and I've finally found an app for my phone that I'm excited to draw with. Color me impressed... and a bit confused. All those features packed on a tiny touch screen can be daunting. Luckily there's an online manual. I sat in Church Square Park today and drew the Hoboken Library, then animated the GIF later in Adobe Fireworks.
BONUS: Christopher Yabsley has a great series of pixel art tutorials on YouTube, as well as a few covering the software Pyxel Edit, which is great for making 2d game sprites. Here's a great run down on what pixel art is (and isn't) and explains concepts like anti-aliasing, dithering, banding, jaggies and more.