Choice 1: A Nintendo DS with a flash card and Animanatee is my choice at the moment. It allows for a lot of colors in its palette, and changing a color's values across all frames is easy. You just tweak the color's values in the palette editor. It has two layers (but one must be cleared each time if you want it to be different across frames) It supports masking, remasking, many brush sizes accessible by a slider, and is a really slick animation program. You can animate anywhere from 1 to 30 FPS. It has quite a lot of undos and redos too! (And the buffer stays even when adding, deleting or editing different frames, unlike EZtoon) This program is super easy to pick up.
Animanatee Cons:
1. Getting an image file is tough. Being an animation program, it only exports AVIs. You must run your AVI in something like irfanview that allows you to copy a frame and then paste it to get an image file. You can also drop the AVI into something like microsoft gif animator, and it should read the frames as normal.
2. Because of DS' screen, Animanatee only allows you to choose 32 scaled values for each channel (RGB) rather than 256
3. Picking colors with RGB values is not so easy. I taught myself to do okay with it by seeing how HSV sliders affect RGB values for this program though.
4. Fixed Resolution of 248x194
5. Only 100 save slots for animation. You could use one slot for like 5,000 images as individual frames in an animation though, as long as you made sure new images didn't mess with the old images palette in the same file. Alternatively, just copy them to your PC, and delete them from the flash card.
6. No select tool. You can copy the frame to a new frame, erase everything you don't need, and then use onion skinning with the previous frame to place it where you want, then copy it back. But this is as much fun as it sounds like.
7. You can't import an image into an animanatee file. This one really bugs me, because I like animating pixel art in it better than anything else.
Animanatee is open source, so if you're a programmer you may be able to fix some of this.
Even with these cons, it is actually one of my absolute favorite pixel art apps (and animation programs) including all the ones on PC. It has such a fast work flow, everything is right there.
DS+Flash card is also relatively cheap. Interestingly, the DS Lite and original DS (not the DSi models) have a form of pressure sensitivity, and while Animanatee barely supports it, there is another program called Colors! which is a real antialiased paint program which uses it if you ever feel like actually painting as well. This is an equally good program, that I also like quite a lot even compared to PC programs. I bought a DS Lite just for the art apps.
Media: DS can play mp3s, videos and display images, but it's not particularly good at any of that. And you can't say, listen to music while you're working in Animanatee.
Price = 155ish USD for a brand new DS Lite and a flash cart + 2GB SD card, without shipping.
Choice 2: There is the GP2X Wiz (and possibly later GP2X models)
http://en.wikipedia.org/wiki/GP2X_WizI haven't used it, but it has a touch screen, is open source and has some pixel art apps that SEEM really good. It's an old model of the GP2X handhelds and as far as I can tell, apps written for it have to be changed to work on newer models, so you may have to buy this used, or find a place that sells it new if the pixel app you're looking for hasn't been ported to it.
http://code.google.com/p/grafx2/ GrafX2 has been ported to it. But there are probably issues with it you may wish to look into:
http://code.google.com/p/grafx2/issues/detail?id=383There are probably loads of other pixel art apps for it too, but who knows how good they are.
Again, I emphasize I haven't used it, but it may be worth researching. It's an option many people may not know about, so I'm throwing it out there.
Media: I have no idea. I assume it's loads better than DS for this though.
Price = 150ish USD for the console if you can find it new. (without shipping)
If you have any other questions about DS art stuff, let me know. I can't answer questions about the wiz, sadly.