Funny I just happened to be reading this as I came in here.
http://2dwillneverdie.com/tutorial/vector-to-pixel-building-your-sprites-in-adobe-illustrator/1-Cluster theory thinking.
yup. Making our blotches of color in beautiful shapes matters.

I've always wanted to point out that sometimes designing them less to tell the shape of the object, and more to show off beautiful shapes is a good approach too. Samurai Shodown exemplifies that.
Shin Megami Tensei, on the other hand is the opposite end of the spectrum. Purely functional and minimal.
2- vector art following a grid like it has been said. But I just realized that +restricted angles could be IT. :p

only 90º and 45º for starters much like this MetalGear Portable OPS logo.
http://www.puppygames.net/revenge-of-the-titans/ this game could be an example...except he overdid it with the gradients and smooth stuff IMO
EDIT: How did I NOT think of ridiculous fishing?
http://vlambeer.com/press/sheet.php?p=Ridiculous_Fishing#images3-Limited palletes.

in this respect I think printmaking processes could be helplful. For example Sherrie York who did the print above uses reduction linocut.
http://www.sherrieyork.com/reduction-linocut-process.htmlWhich means that she starts from the lightest shade, and cuts away at printing darker and darker shades until she gets the full picture. I feel that has the same concern over palletes as pixelart without limiting it with a hard number (8, 16, et all)
Notice how this uses gradients without overdoing it unlike Revenge of the Titans.
http://www.linesandcolors.com/2012/12/29/sherrie-york/http://brushandbaren.blogspot.com/Seriously check that girl out :p
http://hifructose.com/2012/10/17/victo-ngais-action-packed-illustrations/This guy has the same quality, no idea if he uses printmaking but he must've at some point ( or is maybe inspired by ukiyo-e)
http://www.kickstarter.com/projects/1499165518/ukiyo-e-heroesthat, of course earns Ukiyo-E heroes a mention :p
The Reductive linocut process can be emulated in photoshop or any program by drawing a big broad shape and duplicating the layer, ereasing things away from it each time a darker shade is implemented.
I used to think recoloring on the fly was unique to pixelart but it's quite possible in vectors, and it's readily implemented in ToonBoom.
4-Pixel artifacts obsession

RGB offsets, scanlines, moire effect, even the tinted screens of magnetically broken CRTs. it all can be used to achieve a great otherwordly effect
http://www.jeremydower.com/ art is a good example, he goes so far as to use R G B lightsources
https://www.youtube.com/watch?v=UUXBCdt5IPgEven in 3d like Tool's "Vicarious". See how it can be a whole atmosphere?
https://www.youtube.com/watch?v=ia6XoAZUUCYCRT+magnets goodness.
5-Sheer Nostalgia and "Voxel Art"
https://www.youtube.com/watch?v=IHrarYI-vo8 Pixel invasion
https://www.youtube.com/watch?v=hoFYEtj2tDw 3D Dot Game heroes
et all, I'm sure you know what I'm talking about.
EDIT:UGH I just realized I missed color ASCII art.. :p I'm sure I'll think of a lot more